Lampray, eels, and leeches fit that bill and are almost never used, and can readily engorge a good deal!

sharks or dolphins.

i vote sharks.

Pigs have no practically no fur, thematically fit fatness perfectly, and can be pretty glossy if they're sweaty enough.

Smooth skin

My Drakkece is a species of fleshy non-scaled dragons that have an extra vessel based system called the aphroditic systen in their body that makes a substance called 'aphrosia' - they are called aphrosia dragons and, not surprisingly, aphrosia is a very powerful aphrodisiac. Their aphrosia tends to become concentrated in their sexual fluids, but it has potential for mutations! In addition to aphrodisiacs, every individual's aphrosia can have other effects too. Drakkece's causes endowment growth! Could also make a fattening version. Could be amusing to combine that with gas! Aphrosia dragons tend to be very colorful, including multi-colored hair being common (most people seem to assume Drakkece's hair is artificially highlighted pink. It's not! She naturally has some pink hairs among the blue!) Aphrosia dragons tend to be hyper endowed though.

Hrmm, more open-ended... I do wish plesiosaurs got more love. Dinosaurs in general too! There are some neat Pokemon or Dragon Quest monster options (I'm making a fat dominatrix lugia gal myself who enjoys excessive lube messes, as inspired by an image by YMBK).

A fleshy Kirin could also be awesome - I don't see many kirin characters. I think some floofy mane would still be nice though :p

Maybe a frog? Like a poison dart frog, they're shiny and cute.

I also want to suggest jellyfish because they're cute and squishy and there just aren't enough jellyfish characters.

I'd vote for a pig, as well. You might find that a bit boring, though.

lobster

Thinking Gecko, Frog, axolotl , Ornate Box Turtle, mantaray

Salamander perhaps? =3

One of those hairless cats would be interesting.

A sphynx cat, naked mole rat, a skinny pig or maybe a peruvian inca orchid?

An Axolotl! :D

I'm all for a pig! :)

SLUUUUUUGGGGG GGGGIRRRRLLLLL!!!!!!

You really need to do a slug girl!