If the sleeping bag’s not too heavy, and you’re happy with it - why not make another pack, with a slightly larger-capacity packbag that would fit the sleeping bag inside? Since you were also testing the pack on this trip, you could also put on/take off any features you wanted, and fix anything else that you noticed. (My guess is that some pre-sleep time was spent, lying in that bag, thinking “that pack would be perfect if...”)

It’s certainly cheaper than a lighter down bag. (I recently bought a 650 fill down quilt because I couldn’t gulp enough times to pull the trigger for a 900 fill quilt. I even got the quilt on sale. My wife was so proud!)