Check out the lumbar packs at places like REI.com . Non-tactical and a wide range of sizes. There are even extra full suspender shoulder straps (strapettes) available for the Mountainsmith versions.
I carry a Mountainsmith Day TLS and have the "Strapettes" which make carrying it easier if it's completely filled up. If it's not full, I just use the regular single shoulder strap and keep the waist belt tucked away. I also have stuff arranged in Cubes that I can put in as needed. I have one small one with food, one small one with "survival gear" such as a knife, Leatherman, matches and lighter, flashlight. . . I can always leave modules behind if I don't need them.