I've just started Kung Fu a little over a week ago.  I'm older (43), big (tall, and still slightly overweight), and haven't done any serious exercise in... well, longer than I care to admit.

I feel like I'm really struggling to maintain even a semblance of the pose.  I'm not able to get my knees down, and I can't even begin to attempt a half lotus, let alone a full lotus.  During meditation, or any of our exercises from that pose, I am struggling to keep from slouching over, and keep feeling like I'm going to roll backwards.

I don't expect increasing my strength and flexibility to be fast, but I'd like advice on what I can do at home to help work on this, to maintain steady and efficient progress.

What specific exercises should I be working on?