Training in Thailand can be hard, the heat can be brutal. You will get used to it. Drink lots of water and watch your diet. Run lots, when I first went, I couldn’t run 100 metres, by the time I left 3 months later, I was running up to 10 kilometres a day. If you can, start the roadwork before you go. In the ring, those that get tired, get knocked out.
There’s plenty more gyms on the Island of Phuket then my first trips. The original gym I went to doesn’t exist anymore. At that time, there was 6 and possibly more that I wasn’t aware of. Today I believe there might be 20 or more. The majority of them that cater to the foreign market are around Rawai and Chalong. Amenities are plenty, traffic can be a nightmare though. Again, you’ll get used to it.