If you want to keep him as a Bovyne, then keep him as one. I think they're really adorable. :) Also his name would actually suit the Pet.

These three are my favorites, so I'd totally vote for one of them! Maybe Galactic for you since you mentioned Chibi/Spectrum already?

tbh the name makes me think of a christmas themed pet, so if that's something you're interested in you could go that route. like, one of santa's reindeer or something… but maybe instead of a reindeer, a reincow?? in which case angelic could do nicely, but the angelic bovyne actually loses the cute jingle bell in favor of a more classic instrumental bell… so maybe galactic? i would definitely suggest a color that retains the jingle bell.

I agree with that the Boyvnes with actual jingle bells seem to suit the name Jingle the best. As for theme/color ideas: Jingle does sound like a good name for a Christmas pet and for that theme I think the Silver Boyvne would be cute since it has a silver bell. (Silver Bells is one of many Christmas carols that I like.) Galactic would also work since Santa travels at night to get to everyone's homes and a starry steed would be camouflaged, yes? (Maybe you could come up with some kinda of Subetan lore that has Melody using Boyvnes to deliver gifts and Jingle taking the role of Rudolph or one of the other reindeer. -shrugs-)

Jingle also makes me think of those cat toys with the little bells inside and the more obvious path for that idea would be a feli not a boyvne but maybe Jingle just thinks he is a cat OR he has cat buddies who think he is a great big cat toy with his bell and swishing tail. I would suggest the Chibi Boyvne for this concept. (I am a cat person so this idea appeals to me greatly. LOL)

After all the suggestions the others have made I have to make this suggestion: Cherry would be a cute color for Jingle. (I like the Sweetheart Bovyne with the name too).