Pattaya and Jomtien are very similar as they are next to each other and the main attraction is the bar girl scene with a lot of sex tourists. I wouldn't swim in the sea there either.
Hua Hin is a nicer place IMO with cleaner beaches, but the population is mainly retired expats.
Phuket has a bit of everything including a lovely old town and nice beaches.
Krabi is lovely, but I think it would get boring quickly if you lived there and the main resort area gets very busy in high season.
Koh Samui has a young vibe and nice beaches, so it could be a good choice for you.
Places like Samui, Krabi and Phuket are much more expensive than Pattaya/Jomtien/Hua Hin, if that is a consideration.
As others have stated, travel around and see where you like.
If you are over 50 and intend to apply for the non o retirement visa, it makes sense to apply for the visa before you come to Thailand for a couple of reasons.
1. It makes it much easier to open a bank account in Thailand.
2. You do not need to have an onward flight booked.
you were lucky, but as always this is Thailand so it varies between offices. When I did mine a couple of months ago, I booked and there were about 30 people waiting when I got there! Without an appointment I doubt you would have been seen that week!
If you believe the nonsense on the Internet you will think that all British people eat is beans and fried breakfasts!
You can get food from pretty much anywhere in the world in most places.
The food in the UK is good quality with excellent restaurants everywhere. Of course if someone wants trashy food they can find it, the same as the USA.