Hi! Oh how I understand your post... I was so active (like you in the gym, weights and cardio) Now with the back pain I have been pretty much immobile for over a year(and I'm only 30!). It's so hard and depressing... I just started Methotrexate and I am hoping that should help and allow me to be a bit more active. And recently a flare up came on in my knee so I have been using crutches for 3 weeks!!
Suggestions...and they may be ones you already know, but I like Leslie Sansone videos...she does the Walk Away the Pounds videos. They are super basic and easy on the body but she does incorporate light weights into her program.
Another one is water aerobics. I did this after having my knee surgeries and while I'm not the biggest fan, it made be feel like I was at least doing something. (I can't stand swimming laps) and the last thing, which I saw someone already mentioned, was pilates. I was doing pilates but with the sacrolitiis it started causing me too much pain. But I hope to start up again
Diet is also important but I understand what you mean by also wanting to be active...not just for weight but for your mind too! I feel so much better after working out!! I miss it!!
I wish all you ladies the best! Hang in there and don't lose hope (I know my hope comes from the Lord, just knowing he sees me and takes care of me)
Have a nice week!