So far none of the characters I've tried have felt like melee Fox, but hands down the most 'melee' character is Pichu. She plays like melee Pikachu but so much better with the speed, combos, and shield pressure any Fox main would love to have. Pikachu by contrast feels like a mix between Smash 64 Pika and brawl Pika. Pichu's bair loops are like Falco pillar combos and her edgeguard game is easily the best in ultimate. Look up some Void vods, Pichu is the nuts,
Inkling is a 'melee fox' distant second with movement that feels fantastic and a similarly impressive edgeguard game. Gameplay wise she feels more like Doc or Shiek with a meaty back air that is fantastic for spacing and eating double jumps with combined with a grab centric combo game (the Doc comparison may feel weird but I play her in a very similar way to my melee main).
Wario is like some unholy melee Jigglypuff/Mario lovechild that has the fantastic aerial drift and attacks of the former with the potent anti-air and juggle tools of the latter. If you ever enjoyed the guilty pleasure of getting juicy rest set ups in melee but couldn't bring yourself to endure the eternal scorn of being a Puff player, Wario is your B.
Lucina feels like a great option for melee players who like to dabble with Marth. Her moves are very similar and launch opponents how you expect, She has a beautiful dash dance, a great edgeguard game, and really rewards melee fundamentals. However, many of the nuances of Marth's gameplay are lost in translation and I expect this will frustrate Marth mains, hence the recommendation of Lucina for casual Marth enthusiasts.
Roy and Chrom will likely feel alien to you at first, however they both rock a fantastic hyper aggressive play style that can overwhelm your opponents with pressure and crazy frame data. Roy is the superior option imo if you're coming from melee and can't resist going offstage to gimp an opponent with your Roy boy noodle, but Chrom is extremely powerful too. I feel like their playstyle is much more Shiek-esque than Marth/Roy-esque, maybe that's just me.
Responding to other suggestions:
Wolf is very powerful and has a nair centric neutral and fantastic juggle game that is similar on a surface level to melee Fox but imo the two don't match very well. Optimal Wolf play often involves being grounded and being very patient (look up Zackray for evidence of this) with ledgetrapping and 2-framing comprising the majority of his edge game, which as a melee player has been a huge turn off.
I feel like I need to do more research on ultimate fox because I don't quite understand how he works in this game, but for the most part it seems like he revolves around dash attacks, nairs, and utilts. You can shine to gimp! But it's not nearly as good, and you'll likely struggle adapting to all the changes to the character. He is definitely a very powerful choice in ultimate but most melee players I've seen have swapped to completely new characters to prevent their melee experience interfering with learning their new character.
I mentioned earlier that ultimate pika is closer to smash 64 and brawl Pika than melee Pika. His combos are less potent and intuitive than Pichu, and you're going to really miss having melee Pika's nair for offstage gimps and neutral. Using quick attack cancels for a unique combo/approach option will likely be less intuitive as well. so I recommend Pichu over Pika heartily. That said I've personally been grinding Pikachu as I prefer the character's ability to play a mix of offensive and defensive styles while not dying as early. Jury is still out on which Pika I main, but both are dope.
Finally, if you are ok with playing any character that feels like 'melee' instead of just 'melee Fox', I feel like you will enjoy any of
if you enjoyed their playstyles in melee. D.K., Ganon, and Young Link all feel very true to their melee playstyles, just with some new buffs/toys to work with. Link and Ness have experienced more significant gameplay shifts but are very powerful and will still reward any melee experience you have with those characters.