This post made me look at the specific true polymorph restrictions.
Fun things you can still do: Permanently polymorph your familiar into a tressym. If you have an Imp familiar, permanently polymorph into anything CR1, my favorite is Dryad since its charm ability isnt an attack, or an acolyte, for bless.
Transform a large inanimate object into an invisible stalker or clay golem. Both of these creatures state they have a permanent bond to their creator.
Fun things you can still do: Permanently polymorph your familiar into a tressym. If you have an Imp familiar, permanently polymorph into anything CR1, my favorite is Dryad since its charm ability isnt an attack, or an acolyte, for bless.
Transform a large inanimate object into an invisible stalker or clay golem. Both of these creatures state they have a permanent bond to their creator.