i know what you mean, its not nice seeing something like that. after all, we wouldnt wear something so tight it left red marks, so why should your baby,right?!
You could try loosening the waist a bit, so that the leg holes are bigger (or rather leg hole, if its just one side). Shouldnt make too much difference if the waist is a bit baggy. its the legs you need to be more concerned about tbh.
Have you tried a large slinki minki? the large standard is too big for my son who is 3 years old but the slinki is great - i bet that would work for you. You could swap your new ones for large slinkis instead then