"Wish I could start doing"? Of course you can, but wishing only will not take you too far. C´mon and paint!
When I try something without reference it becomes very asymmetrical and it doesn't look like it's part of the environment that it's in.
I have trouble drawing poses straight out of my head.
Then, don´t. References are there to help us. Use pictures and have always a mirror (or someone willing to pose for you) nearby, and sketch the damn pose until 1-it looks as you had in mind and 2-you UNDERSTAND the pose. Repeat the process ab nauseam.