My suggestion if travelling on your own is to find a good losmen (Suri Wathi in Jl. Sahadewa Legian has always been good) and you will be sure to meet other travellers. Legian/Seminyak areas are probably the areas to stay as they tend to be busy and you are perhaps more likely to meet people more readily. Kuta is not my favourite area by a long shot so it's not a place I'd recommend to stay.

Not knowing your budget it's difficult to suggest places to stay but a losmen is more the type of place where you are likely to meet people. With all due respect to larger hotels, many people are travelling as a group or family and tend to stick together.

There is a yoga centre in Ubud as far as I know but I have no personal knowledge of it so I can't help you on this question. An internet search will find some information.

Good luck with your trip and have a wonderful time.

Catherine