I'm growing trollius from seed without much luck. Out of a whole seed
packet only 4 germinated and one of those has subsequently died. One
is doing very well and has been repotted onto the kitchen windowsill
but is growing very slowly. Is this normal for trollius? Any tips?

Trollius is among the hardier plants. I suggest that you harden
off your survivors and put them outside. They'll be much happier
in the cooler temperature.

Great, thanks so much everyone! Yes, I've been pampering them to
death with moisture and warmth. Outdoors and hardiness it is for the
little beggars now.