New to the community 50 gone 50 more to go

I'm a 20-something mom who is new to the forum. I have lost about 50 lbs and am trying to lose about 50 more. I want to get fit for my health, my husband & family, and for my self-esteem. Currently, I am reducing my caloric intake while improving the quality of my foods. I am also working out for about 30 minutes 5x a week at a high resistance on the Octane 37 Elliptical. I want to add in some core exercises? Any recommendations? I've only recently had a baby so my stomach is very weak and loose. I want to tone it up and improve my core's appearance. Thanks to everyone, and I look forward to getting to know you all!