Hi GQ,
I do pilates regularly and have tried several different teachers, all of whom knew their stuff but found the best way is to have sessions with only 2/3 together as the teacher can then cater for your particular needs.
It can take a while for you to get into the swing of it but you should end up with better posture and less backache.
There are many different exercises and a lot can be done on a mat but if you go somewhere that has equipment [ reformers etc] they can be very helpful.
Cecilia