What are some of the best, less used bulky pivots in the tier? (In your opinion)
I'm going to take this literally to mean a bulky pokemon that can pivot:
Chansey is probably the bulkiest pivot with Teleport, and I've been seeing an uptick of usage for it on balance teams instead of just being a stall staple.
Other than that, people have used bulkier Scizors with U-turn, bulkier Rotoms (wash and heat) with Volt, bulkier Moltres with U-turn, etc. There's also some rare usage of Mew using Teleport as well.
Finally, you can use some Regenerator mons like Amoonguss as pivots, and even give them Eject Buttons.
Obviously these are very specific to the type of team you have though, so if you wanted more help/suggestions building with them I suggest asking in the PS UU Room or visiting the UU Discord.