I’d suggest sell and rebuy: new technology is way cheaper than you may remember it 10 years ago - transport / insurance / import duties / worry etc just not worth it
Most people here never cool the entire house - living rooms during the day, occupied bedrooms at night. Single split systems, one per room is standard.
There will be a huge difference in energy consumption between new 5 star energy rated appliances through vs older appliances.
And of course the area of Thailand you choose will make a difference.
An average house in Thailand is a standard 1,500 square feet 2 storey 3 bedroom moo ban house. My wife and I rented one in Phuket that was about 5 years old (so pretty efficient appliances) with our son (so 2 bedrooms chilled overnight and living room during the day) and a typical electricity bill was 3k-5k per month.
If you are buying or building a house you can upgrade your appliances to 5 star, add solar and your bill can be close to zero.
Or you can buy a larger house with old appliances and your bill will likely be 15k per month or more.
At this time of year the air is pretty awful all over the region, but other than this brief period Phuket / Krabi / Phang Nga have very clean air and a temperate climate year round.
I don’t think you need to worry about being taxed on your pension in Thailand - not a tax lawyer but that seems to be the consensus.
Farang bashing in the media is a current fad - will pass and return from time to time, but doesn’t affect daily life.
Immigration is straightforward if you understand and follow the rules.
In short, I think your’re worrying about nothing much
As you grow older your health insurance premiums will rise - decent inpatient cover for a 50 year old will cost THB70k a year and will steadily rise year on year.
As most people have stated there is a huge range of standards and costs of living here.
GBP200k is about THB9m - in popular expat areas such as Phuket / Samui / Hua Hin that will buy you a house or decent condo and a new / near new car without any / much change.
GBP1600 is about THB70k per month. Say 10k for health and 15k per week for everything else. Depends what you like doing: a nice meal with wine can cost 2k-3k, a round of golf 2k-5k, a night in a cheap beer bar with food maybe 1k. A massage 300-700, an afternoon at the beach 500, an afternoon / evening at a beach club 3-5k, the list goes on.
So in summary I agree with you, the GBP200k/1,600 per month is a bit tight. Double that and you’re very comfortable, triple that and you’ll have a fantastic life