The needle size is probably shredding the thread. There is a difference on the needle eyes.
Try a 90/14 topstitch needle with a 3.0 stitch length. We used these in our bag class which used the very thick bag batting. I used poly 40 embroidery thread to quilt the pieces and for sewing the bag together. Same thread in the bobbin to match the fabric on back. This is my go-to thread type for many projects and seldom have any issues. Try a spool or two to see if you like it.
Do you have a walking foot? It will help feed the layers through the machine.
I trim out the batting from the seam line to reduce bulk. Cut right outside the seam and not any of the stitches.
What type of straps are you making for bag? I also make them so there is no bulk in the seam lines. If you need help with them let us know.