What type of visa should I get for training martial arts in Phuket?

DM you let me know you get

Unless you are staying over 2 months then you won’t need to get a visa, you’ll get the visa exemption when you arrive.

For Muay Thai there are alot of gyms in Chalong, there’s a street called the fitness street or soi ta’ied that you can look up.

These gyms aren’t the best tho but they are more accommodating for tourist.

One of the best gyms is ran by Bryan Dobler an American called Phuket Muay Thai that’s in Rawai.

The best traditional Thai gym is in Kathu called Sor Dejdamrong Muaythai or closer to Rawai is Sinbi Muay Thai Training Camp - Phuket, Thailand ค่ายมวย ซินบีมวยไทย

The best visa will depend on how long, which you don't say.

The best place to stay will depend on what school you are attending.