i had an old car and used a clothes pin too. then changed to a binder clip. then got my van and could lock the seat belt one inch from my chest. loved that. now have a Honda and cant' do that. but don't need the clothes pin either. the belt is adjustable on the side frame of the car, up or down, depending on one's height.
I might suggest a firm pillow for your seat. that will raise you up a bit and might be more comfortable.
oh yes i did make a cover for it too. velcro closing. you can buy them also.