someone will undoubtedly explain the exact terminology (OA or OAX or whatever). There used to be a multi entry one year, that in effect was 15 months that required insurance and financial criteria. That also (or instead) now requires a bizarre medical stating that you don't have elephantitus and some other diseases that would actually require months of tests I believe...but in Thailand you'd probably get a 1000 baht chit from a GP. It also requires a police check (which I did do before going the DTV route instead. I asked my GP about the health check and the NHS won't cover that but the clinic would issue one. DTV was easier , 5 years, 180 days at time and good value....ultimately easier and actually what I do
for me I showed my business, I have a website and a company presentation. I actually showed an investment account as meeting the financial requirements (which includes a SIPP), they also asked for some other proof, in my case a tax return (nothing exciting or onerous there). That was roughly it. No insurance requirement, medical requirement etc. I guess that if you established an online presence and showed that you were genuinely freelancing (I explained that I freelance for my own firm) then that would satisfy the requirements. What have you always wished to do? Or maybe you already have a legitimate business. There are other routes under soft power: cookery, language, Muay Thai...
I was going to go the non O route which I've been using a few years. It's changed though and the multi entry has more requirements. I went DTV instead as I have my own business and it was dead easy, 5 years, 180 days at a time and £300...great if you qualify