How do I know I'm improving?

Today is Thanksgiving and I have a lot to be thankful for. I have a wonderful wife and two wonderful kids and am quite blessed.
I'm back in Laredo waiting to go to work again. My bjj continues to improve, at least I think it does. My game has really slowed down and I am starting to make it harder for better players to sub me and get position on me. I am doing better against the fellas with stripes and I am not tiring as easily. My only real concern is that I'm so much bigger than the people I roll with I can't really judge where I am at. I'm usually 40-50 lbs heavier than everyone else. I don't know if it is just my instructors or the fact they are Brazilian or what but they are tight with the criticism. I think I am going in the right direction (I only concentrate on sweeps and defense and try to make everything else secondary). I only hope that I don't make unrealistic expectations for my self. I don't want a belt or stripes, I just want to know if what I am doing is correct tor not. This is all a mystery to me but I am reading up and I need to take the advice I give to others, and just let it happen.