Is there a long-term visa option for retirees under 50 in Thailand?

Is there an appropriate visa to stay long term in Thailand for someone retired but under 50?

Not working, just living on a modest life from overseas saving and investments.(in my case about 40-50,000 THB a month)

P.S. Thanks for the helpful comments on my related post two days ago. There were some interesting suggestions there, but no ideal solution. I also inquired about METV, but the London embassy told me that requires a letter from an employer, so not possible for me.

What I am asking now highlights maybe highlights a fundamental issue: for some people there just doesn't seem to be an appropriate visa for their situation?