Do what we call ‘Mermaids’. So your back resting on your forearms draw your feet up lower them down just as far as your pelvis does not tip and bring them in a circle around and the opposite direction. This is doing two things it’s getting your body to understand how to keep your core engaged, so that when you’re in in-stable environment like the fabric you can maintain your strength. Like you did the mermaid on the floor you’re going to do it on the fabric you can climb once you’ll pull in to a position where your body is in between the fabric you’re gonna bring your knees up feet out then you’re going to go the other way and then come down. The ‘mermaid’ is extremely difficult to do cleanly. It’s not the number of mermaids that you do it’s the quality of the movement so if you can only do one cleanly then that’s all that you’ll do and you’ll continue to try and add onto that one.