I struggle against Corrin, Bayo, Falcon, and Fox for the most part.
Alright. Surprised you didn't say Sheik, as she is commonly cited as Cloud's only losing matchup that we are confident of. While you may be better off hitting up the Cloud Boards and asking in/reading their matchup thread, and figuring out the matchups, that seems to be what everyone is saying. I know that's not what you're looking for, so let my try and see what I think would be a proper pickup for your situation.
Diddy does seem to deal with the bulk of these characters, though I am unsure of how he does against Falcon and Fox. Marth goes even with all of them, more or less. He's also a sword character if you are looking for that. Let me just break down each character instead, because why not.
Corrin does decently against Cloud, he loses slightly imo. He's pretty easy to juggle and pressure if you know what to watch out for, and he's also pretty slow. Loses to Diddy, Fox, Mewtwo, Cloud, Toon Link (imo).
Bayonetta versus Cloud is kinda up in the air at the moment, but she has very very strong gimping tools and strong horizontal combos that back those up. Kills late outside of gimps and Witch Time reads, neutral is okay. Susceptible to getting lamed out. Loses to Diddy, Mega Man, Cloud, Mewtwo, Toon Link, Lucas, Ryu (this spread is very theorycrafty, not for sure.)
Falcon is a simple character with powerful tools and good mobility. Try not to air dodge much against him or you'll die at 60%. Free gimps on him, but he can also f you up offstage if you're not careful. Loses to Pikachu, Sheik, Mega Man? idk who else, has a lot of even MUs as far as I can tell.
Fox versus Cloud is pretty even at top level, but outside of it I can't say for sure. Fox is very good at pressure and he craps out damage when he gets in. Can't kill off of throws and is easy to gimp. Loses to Sheik, Ryu, Rosalina? Luigi, Marth, Kirby and Dr. Mario randomly do well against him too. He's a very polarizing character capable of getting blown up or destroying his opponent at any point in the match.
Not the most thorough assessment of each, but it gives you an idea. So my suggestions would be
or maybe just pick a character that plays very differently from Cloud, that way you can change how you're approaching matchups or players. So someone like
that's simple but operates differently from your main. For a different approach or learning tool.