Avoiding certain sounds and using other sounds instead will only function for as long as those other sounds aren't themselves becoming part of the stutter. Also, having to constantly find substitutes can be exhausting, putting further strain on your speech performance, and making things worse in turn. Instead of trying to avoid the sounds that are difficult to you, did you ever try working with a speech therapist to help you manage your stutter? There might be improvements you can make to your speech in general there.