You're an amazing person...I cried when I read the story but he looks great. You did an awesome job!
I don't know if it would be too slippery or not, but non-adhesive self liner might work for the bottom of his cage (or maybe part of it, but it seems like what you're doing now is working perfectly, just a thought). It's cheaper than the reptile carpet and much easier to clean. It actually might help him get around a little easier (if it's not too slick)...I don't know though. You have obviously figured everything out and have taken great care of this very special beardie.
Are you still dusting his crickets though? He still needs the extra supplements/vitamins, but at the age he is now he shouldn't need as much, I'm sure others will correct me on that if I'm wrong (please do, I don't want to give the wrong advice).
He looks so happy; you gave this little guy a life and a good one.
Please do report that petstore, that's so cruel and they deserve to be punished for making these animals suffer.
It looks like he has everything he needs and a lot of love and devotion from you. I can't applaud you enough. I don't know what else you need, I'm not located anywhere near you, but if there's something vital, I'd like to help.