Just a bit of advice, please be very careful with doing any straight double leg raises/lowers as ab work, they demand a very high level of strength and control already and if you do not have that, you may be putting your back at risk. Start lower level and work your way up, as a physio I would never advise anyone to start with an exercise like that.

I find pilates quite good, also many people like yoga. I did belly dancing and found it excellent for getting the tone back and also much better abs control, it was great.