varunbhalla

Patong seems like a good choice for you but it isn't really quiet (Barring a few areas in North & South Patong). I would suggest considering Karon or Kata. They have the accessibility to Supermarkets and are relatievely lesser crowded.

You should be able to find tons of mid-range beach sides resorts there. Also, you might want to check out this artcle I used during my trip. These guys have a quiz to recommend areas based on your preferences: https://www.ithaka.travel/blog/best-areas-stay-phuket/

Phuket isn't really the best place for scuba diving, I would suggest going to Phi Phi (It is a 2 Hour ferry ride from Phuket). You will end up paying half the price and experience a much better marine life.

Also, read this thread on quora, you will get a better idea about the dive sites in Thailand:

https://www.quora.com/Where-are-the-best-scuba-diving-spots-in-Thailand