Elevated side planks are one of my favorite core exercises. I especially love them for my pregnant and postpartum mamas.
Here is an awesome little addition if you’re struggling to feel those lower abs in addition to your obliques.

I see the following with a lot of my clients:
Traditional side planks often end up stressing their shoulder more than their core.
The regression of bent knee side planks often don’t feel as though they are challenging to the core enough.
Instead of those two variations try using a bench or a low box for a longer lever while still modifying.
Focus on breathing into your back body and exhaling your top rib down towards your bottom hip. ( Inhale back, exhale front, think of your hip bones drawing together and emptying your air from the bottom up). Give it a shot and let me know what you think