i don't think there's a need to buy any more bags, you have 2 already!
i have the X-L timbuk 2 bag, and it works fine for me, there are two small things you can do to increase the comfort 10 fold on these bags,
1.) on the top and bottom of the bag where the strap connects to the bag is not smooth, wrap a shirt around one or both of them, though the top one is the only one that gives me a little shoulder ache when i have a lot of weight in it.
. . . if you're crafty, sew padding for it
2.) grab an old hoodie, and put it on the back side of the bag, this is padding for your back if you have awkward shaped items, i carry 8 juggling clubs and a large bag of juggling balls in my bag, and it works fine with the extra padding.
the search for the perfect bag is never ending, and costly, just be happy with whatcha got : )
besides, i find the timbuk 2 very comfy as long as you pack it right, and have that hoodie on hand : )