My personal opinion, don't need to spend money on them unless you can afford to go to the best people.

For example, there is one old man in Thailand, really good, used to treat the king. But I can't afford it, the time and flight fares.

I believe you can find such people here in Malaysia, but perhaps not as experienced.

For example, one of the famous chain store here in Malaysia, I would try to catch an appointment with the boss instead, won't go near any of the pupils if I have major problem, probably settle for them only for small problems.

And NO, one is never enough. There's no quick fix. It's all slow process with many factors involved, including personal discipline and determination.

On the other hand, I'd recommend you take Pilates. I know a trainer personally, and I've tried both mat classes and also those with equipment. Mat classes are cheaper, just like yoga mat classes. But if you've got the money to spare, you can go for one-on-one sessions with equipments. I'd say it's really good, especially the equipment sessions.

Posture problem is not about bone problem (usually). It's about your own discipline, and training up the muscles that support you.