Sounds like you're going about it the right way! Doing gesture drawings from photo reference is one of the best ways to build up your visual memory bank for drawing poses from imagination! A good exercise to try during your gesture drawing practice is to draw a pose from reference and time yourself, and once you've finished put away the reference and then try to draw the same pose again immediately from memory in the same amount of time, and compare the two. After doing a few of those you'll start to see patterns emerge where you struggle the most, this is where your visual memory is lacking. You can then target those specific areas of focus in your next studies. Check out the book "How to Draw Comics The Marvel Way." It's an incredible resource of foundational learning for how to draw from imagination. Also "The Natural Way To Draw" by Kimon Nicolaides has an entire section dedicated to different Memory Drawing exercises including the one I mentioned above. Hope this helps!