is right about the looking at the LTR first, if you qualify it is the best option. Just two small notes: 1) Currently the Non O 90 day in Canada no longer requires proof of insurance, even though it still shows on the embassy site. We went back and forth on this with the Vancouver Consulate in August and got the Non O without insurance. 2) To get the affidavit of income you can use multiple methods to prove you can support yourself, it doesn't just have to be proof of pension.
If you do plan on traveling a lot or don't qualify for the LTR, the DTV might be an option to consider. It's multi entry, 180 days/entry and valid for 5 years. You can do an in country extension for another 180 days but no one knows what that will actually entail. It's only been around for 5 months so people will only be starting the process in the next few weeks. Embassies are getting stricter and putting in all sorts of extra requirements recently so it's impossible to know what the requirements will look like or if it will even be around in your time frame.
Once you've figured out what visa works for you, it's easy to do yourself just a matter of getting your paperwork together and applying. Even in country extensions are easy but a lot of people use agents since spending 4 hours in a crowded immigration office isn't the most fun use of time. Join the Canadians in Thailand | Canadiens en ThaΓ―lande group for some Canada specific info.
You are asking for general advice in a very specific visa group and providing no info. You'll get better responses if you ask in one of the general Thai visa advice group where you will get more mileage about different visa options. Then you can start your research as to what suits you best.