I would just send with what you have. When I applied in late feb i didn't attach insurance - they emailed to request. For my 3 month Non O they acceptes free insurance I get with my Revolute card - Thai pass also accepted it.
UK is very easy. As long as you have funds showing on bank statement - UK funds are fine. As already said, all online - they send msg if need anything else. I got mine 2 days later. £60>
In my case, for Non-O 3 month retirement, the UK Thai embassy also asked for insurance. They accepted the Travel insurance I get with my Revolute bank account. I attached the page showing cover and amount.
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