Related question. Is Chiang Khong the closest crossing to Chiang Mai? We've only ever been across to Myanmar or over to Vientiane on previous runs, with Myanmar land closed Khong is interesting.
Imvho take the 60 day SETV in the UK online, super easy process. Then extend 30 days when here. Do a short trip out and return visa Exempt for 45 days, renew once 30 days. Repeat. Border bounce is fine but become a pain, make plan and enjoy a peaceful 90 days to start. Cost wise, the cost of a trip out and back will be roughly 1900 BAHT anyhow when you think transport, food, bits and bobs, maybe a room for a night or two. Good Luck, enjoy.
the application is the same for both, you just need a good reason why you need METV. But I'm unsure of the lead time to entry. Worth checking for sure. Good Luck.