You should check out Hua Hin
It certainly seems to fit your criteria and is very popular with retired Expats and foreigners staying long term..
Quite a variety of different locations in and around Hua Hin to suit just about anyone and a good selection of accommodation options..
Good infrastructure and amenities and good hospitals and medical and dental services available.
There are a couple of Hua Hin Expat groups on Facebook that are a good source of more information..
There is a nice Marina south of Hua Hin as well that is well sheltered up a river that leads out to the ocean.
I have a friend who uses this Marina and been there several times.
Here is the website for the Marina..
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