Wise guys makes seats with an integrated shoulder belt. Not cheap, but you have to decide what your safety is worth. I should consider this as an option for my car, but I already have racing seats with dual shoulder straps. The racing seats are awkward to use, though. The shoulder straps have no ratcheting mechanism, so once you're strapped in, you can't lean forward to help look to the right, for on-coming cars. It's tough to look cool and be safe at the same time.
http://www.wiseguys-seats.com/wp-con..._List-2012.pdf
I believe this was somewhere around 2015, Rick, Rosie and Johnboy
John Norton aka johnboy