... that wouldn't have been from the Thai consulate in Hull by any chance? I had a few from there as it was well known they were quite liberal in handing those visas out.
... 2 months seasoning before application but you can also extend your 60 day visa exempt entry by 30 days at the IO for 1900 baht to give you more time if required.
... you can buy at the immigration office or at the airport before you depart. It only takes about 15 minutes and you get it before you stamp out through immigration. If you do a group search "re-entry permit" you will get all the info you need.
... I had the 1 year multi entry for a few years but I was travelling out and in a lot for work so the 90 day max wasn't an issue. Since the end of 2020 I've had the 1 year extensions after my initial 90 day non O visa and just get a re-entry permit if I'm travelling now.
Reading between the lines, it seems you picked the wrong visa. A non O 90 day single entry would have been better as you don't have to leave the country. Just get a 1 year extension before the 90 days finish then you are good to stay for 1 year without leaving. The 1 year extension can be renewed every year indefinitely providing you meet the requirements. If you need to leave you simply get a single or multiple re-entry permit before you leave which allows you to keep your extension alive.