Safe Ab/core workout for low density bones

I’ve been diagnosed with osteopenia in my spine and hips. I’ve altered my exercise regime to include more weight bearing and weight lifting to help build stronger bones. However, I’m finding it difficult to find an ab/core routine that does not include moves that are dangerous for my condition—moves that round the back, arch the back, and twisting motion. That means no crunches, bicycles, Russian twists, cat/cow, etc. Does anyone have any ideas for a safe ab/core routine?