Agreed that Morphagene is too big for a small case
There's a ton of videos on YouTube with experts creating nice small systems using the Palette case. It's much more difficult than it looks!
Everyone should get Pam's eventually, but since you already have uO_C it might be better to go with 1u Steppy until you get a bigger case
Here's my suggestions for good compliments to uO_C and Plaits:
1u Steppy for gate sequencing
vpme Quad Drum or Erica Synths Sample Drum
Ghost or FX Aid
Delta V or Maths for envelope generation