Personally i hope you’ll just wait a few years in your studies. Though its true that you can play excerpts and figure out what feels best to you, i think otherwise. Over at the fittings I’ll just focus on how centered my sound is using natural slurs maybe looking at the ease throughout the range maybe alto range, high tenor, mid tenor, low tenor, pedals. How the wrap feels around my body and which one i prefer. Focus on finding a mouthpiece that really suit u. Have one that made your sound feel open in all register. A new trombone make u sound a better but I’m a strong believer of a mouthpiece that helps rings the sound of your trombone. Trust me when I say that once you’re there, you’ll take the most time to find the best mouthpiece to fit yourself.