Especially with the addition of pillager raids, it would be interesting if the Iron Golems were, say, actually useful during a raid. Seeing as the villagers are peaceful folk, I've included concept art for new iron golem types in the Attachments Section. (Since there's a max of five attachments, I've also included links to additional rusted variants)
-Normal Golems would rust if exposed to water, decreasing speed while increasing damage dealt.
-Little Golems would be a more common type of iron golem that deals a small amount of damage, but is faster and spawns more frequently. You could make one with a single block of iron and a pumpkin.
-Tall Golems would be unique to larger villages, and would be able to use a projectile attack. They would require three blocks of iron stacked on top of each other, and a jack o lantern.
-Big Golems would be a rare find in larger villages, being harder to kill and generally tougher. To make one would require even more iron than a normal golem.
-...Player golems? Not sure what these would do our how they could be used. Make like a snow golem, but with iron?
Mmm... I'm not sure how I feel about most of these, but I do like the idea of the "Rusted" Golem. Perhaps Golems exposed to rain/water for extended periods have a chance each tick to become rusted, which slows them down and reduces their health somewhat but increases their damage & lets them inflict Poison with their attacks.
I also wouldn't mind temporary modifications to Golems. Perhaps, for example, you could use a Lava Bucket on an Iron Golem to make it into a Molten Iron Golem. The transformation deals 40 damage to the Iron Golem, but it subsequently moves faster, lights targets on fire, and can shoot fireballs for some duration of time. An Armored Golem could be made using a Turtle Shell on it, which like the Rusted Iron Golem moves slowly but takes little to no damage even from the heaviest attacks for a short period. You could use Slimeballs on one to make it into a Gummy Iron Golem for a little while, which deals severely reduced damage with its attacks but also applies considerably greater knockback to anything it attacks. Finally, using a Nether Star on an Iron Golem temporarily turns into into a Resonant Iron Golem, which applies all the buffs granted by a beacon to those within a 10 block radius for a short period (60 seconds or so).
Using that model, you could make Rusted Iron Golems by using a Bucket of Water on them, after which they would become rusted for a brief period. Regardless, I think temporary buffs to Iron Golems is better than just making a bunch of new permanent Iron Golem variants, particularly since they mostly don't really do anything a normal one doesn't do already.
It would be interesting if you could further modify existing iron golems- it just seems to me that, considering how expensive they are, they really aren't that effective in combat. I like the idea of temporary buffs too- rusted and molten golems. Maybe bone meal could be used to make 'Bloom Golems,' which would be weaker overall, but would heal faster overall. Maybe also an ability to use various metals- (Gold, Netherite, etc.), to upgrade golems further?
As for different golem variations... yeah, probably not necessary; I mostly just wanted an excuse to try out a new modeling engine. I like the idea of little golems though- if only as a cheaper, weaker alternative to the big guys. On the other hand, dogs do sort of fill the niche of combat aids.
Added some more concept art- just retextures of the basic golem skin.