Core Workouts

Any of you mommas have any advice on core exercises during pregnancy?? I had a c-section with my first and I had no core strength after and could hardly sit up in bed without a struggle.. I want too be sure I'm doing what u can to keep my core strong with this pregnancy. I'm not worried to much about getting my abs back right after my baby is born, more just want to be able to function normally since my daughter will be about 18 months and keeping me hopping... Any input or advice is very appreciated! Thank you!!