Pellon makes a great batting/interfacing, I use 971F (the fusible one) and it works great....since you fuse it to the fabric, you don't have to do a lot of quilting unless you choose....I usually only do diagonal lines about 2" apart.....If you have to take your bag apart to fix the handles, you could do some additional quilting to make it a bit stiffer.....after fixing the handle placement, you could also add some ties to the outside of the bag, like the bowtucks bags....a very simple thing to add that will close up the top of the bag a bit (doesn't affect the capacity of the bag itself) and will add a bit of pretty detail....you also could add a large button to the outside and a fabric loop on the opposite site for a simple closure....very pretty bag and lots of easy fixes to your problem!