Welcome to this forum!
You might perhaps be better to inquire at euroga.org, there's a fair deal of single pilot IFR flyers around there. For as little as I am aware, the answer might be decided by pilot (i.e. license) limitations or by aircraft equipment limitations or by airspace limitations - SERA might have an important role to play. Not my cup of tea really, but you'll find out.
One thing that I seem to remember: several FIR's require a (certified!) auto-pilot for single pilot IFR operations.
Good luck, and do keep us posted!