Depending upon where you are travelling to.. it might be cheaper to book another flight leaving on 31 March.. or perhaps investigate switching your existing flight to one day earlier.. if the airline will allow it.
You are going about it the right way imo.. get the 60-day visa before you come.. as mentioned elsewhere you have the option to extend it by 30-days in-country.. which will give you plenty of time to apply for the 'retirement' visa in person.. your intended hotel should be good enough to satisfy the address question.. though you didn't mention whether they require evidence of a booking.. if they do then use an app like Hotels.com to book a room and select a hotel that offers payment on arrival along with free cancellation.. usually this means 'free' if cancelled before a specific future date.. so it should cost you nothing to produce evidence of accommodation.. and there are websites you can use to buy a 'temporary' booking on a flight for a nominal fee (eg. $10-$20) which is then automatically cancelled.. but you will again be able to evidence a flight since you'll have a booking confirmation.. but in tandem these 2 approaches should get you through the hurdles you've been facing.. and having gone through the process of obtaining and extending a long term visa in Thailand myself.. I'd advise you to avoid using an agent and to do it yourself.. they are an unnecessary expense imo.. if you meet the criteria you won't have any (insurmountable) problems getting your retirement visa.. you also need to be aware that using an agent could lock you in to using them repeatedly.. ie. for every future annual extension.. since you will be blind to any corners they may have cut to accelerate the process.. and this could cause you problems if trying to switch to handling the next renewal in person.. agents are generally used by people who do not fully meet the criteria for the visa they want.. said people needing someone with a 'friend' in an official capacity who can smooth the process by overlooking any deficiency.. many agents have such officials on their payroll to short-cut the process for their clients.. and if you are in this category you can argue that agents are good value.. that is provided you have the financial resource to pay them year on year to handle the renewals.. or perhaps someone has limitless resource and despite ticking every box (legitimately) they are simply too busy (or lazy) to apply themself to the task.. of course there are situations where agents may represent the best solution.. eg. such as getting marriage certificates translated and validated.. but the fees attached to these services are fairly modest by comparison.. but you need to understand the risk versus the reward of engaging them for any given task.. and you should do some research before making a decision to use one.. i wish you the best in resolving your dilemma my friend.
If your Thai motorcycle license is recognised under Uk road laws.. meaning it gives you the legal right to ride a motorcycle in the Uk without restriction.. then it would be reasonable to assume your travel insurance would be valid in the event of an accident whilst riding a motorcycle in Thailand.. however this is not the case since there is a restriction in place that limits how long you could ride in the Uk with a Thai license before being compelled to take a Uk test and obtain a Uk license.. just as there is here in Thailand.. and even if said restriction did not apply.. i would say validity of cover would also depend upon when you obtained your Thai motorcycle license.. because you would have needed to hold it at the time of buying the travel insurance for the cover to be effective.. meaning if the motorcycle license was obtained afterwards.. and is dated after the acquisition of the insurance policy.. then the insurer is unlikely to extend coverage and could deny a claim.. so it would be unwise to rely upon it in these circumstances.. when all is said and done i do wonder why you need to lean on your travel insurance in this scenario anyway.. since hire bikes should come with insurance that you can usually top up for more complete cover.. and if you own a bike it should have insurance.. it's fairly inexpensive in Thailand.. and if you are looking to ride here extensively it makes sense to be properly covered under a Thai insurance policy.. if you were ever hospitalised as a result of a motorcycle accident the last thing you want is to be denied treatment because your travel insurance is not valid!
Are who still in business.. do you mean Expatfone.. as mentioned, I'm a current subscriber.. meaning i use the service myself.. and I'm not aware of any issues 🤔
I guess you could get a friend or relative living in the Uk to activate a new Uk sim card for you using their phone.. then mail it to you in Thailand.. but if you already have an active Uk sim then a virtual mobile phone is a good solution 👍
If you have a Uk mobile number that you want to keep 'live' after moving to Thailand.. and want to avoid periodic top-ups on a PAYG sim.. or contract fees for a tariff you cannot use abroad.. then consider moving your number to expatfone.. which gives you a virtual Uk mobile that is accessible via an app.. so it can be used on any handset or tablet etc.. and you get free calls to Uk landlines and mobiles (from Thailand) without ever having to disclose you are out of country.. very useful if you need to call your Uk bank or they need to call you.. and you can send and receive sms messages as well.. so solves your bank verification sms concerns.. there is a monthly fee (works out at about £2 weekly) but it's much cheaper than any alternative i could find.. and if you return to the Uk to live.. you also have the option of porting your number out to another service provider.. so you don't lose your number.. for me it was a no-brainer really!
The problem is connecting a new Uk sim to the network to establish it as a 'live' number.. i think you would need to do this when you are still in the Uk.. ie. before travelling overseas.. i could be wrong but i believe trying to connect via a local network here using roaming is unlikely to work for new sim registrations.
And with ten zillion atm transactions daily they will surely have the resource to handle such a reporting structure.. having worked in the banking industry for a good portion of my career i can tell you such a system is frought with problems.. and by the time somebody actually gets close to a working (meaning reliable) model.. income tax as we know it will have been abolished.. and will have been replaced by a single 'purchase tax' applicable to new items only.. which will be a flat rate of around 15% in most countries.. and tax returns will become a thing of the past.. so in that sense this discussion becomes irrelevant!