You could get the ZZ Top straps. Then you can spin the guitar round...
I've ended up using leather straps again if I can as prefer them, however, they slip easily I find, but that is also dependant on use, they do need to be worn in. The nylon ones can chafe, used to have that a lot. The leather straplocks I switched to are nice, but all need to be worn in as they are quite stiff to start off.
You can always try and put it in some kind of sheath material on the bit nearest to the neck over the shoulder with some padding s it moves freely inside that, but is softer against the neck.
Other solution is to wear a shirt or something with a collar on it to act as a barrier.
Have you tried thinner leather straps? The extra wide nylon ones aren't as quick to reposition as the thinner ones due to surface area friction and all that crap, and the same is likely for the leather straps. Also, smoother the leather underneath, the less friction it's going to have.