I'm not disciplined enough to do the PB fitness exercises on my own so I take a class called Pump + Abs that does a lot of core fitness things. We do squats and planks and things like that but we sometimes use small weights or bands to add intensity or stability balls or small balls to support the back when doing ab things. I know a lot of people scoff at such things, but since I had to start at zero basically, it's been very helpful for me. Plus being a class, I just show up and follow the leader. And since there is an instructor, I can ask questions when a particular movement is hurting me and she'll help me either modify it so it doesn't hurt or tell me what I'm doing wrong.
Female, 5'3", 49, Starting weight: 163lbs. Current weight: 135 (more or less).
Starting squat: 45lbs. Current squat: 162.5 x 2