1) Health insurance - You can get a free quote on the wrlife website without giving them any info. Most others want your contact info first. But you have to realise that you are most likely to excluded coverage on many things. Like if you take blood pressure, cholesterol, blood sugar meds you will most be likely be excluded coverage for heart attacks, strokes and such. https://www.wrlife.net/ You are probably going to find that health insurance will take about half of your budget and you will still be on the hook for many medical costs.
2) food - if you eat cheap thai food you can have 3 meals a day for about 7,000 baht a month. But it can escalate quite abit otherwise. In Ratchaburi there is a restaurant that has the best steaks I have had in Thailand. But then you are talking 1,200 to 2,000 baht for one meal. Even eating falang food at home is going to cost you more than eating the local prepared food.
I think I could live on 30K/month if I was by myself and lived a simple boring life. But that would not cover anything more than basic medical costs. My wife and I budget about 120K/month and sometimes exceed that.