What base are beast of nurgle i hear its 40mm but feel free to correct me on that

Would it be legal if i used a Chaos Spawn or would i have to use green stuff just to change it a bit?

Is there any info out there at a hint of a plastic beast of nurgle?

I dont want to use plague Toads from forge world due to they are too big but are there any other models wether it be forge world or games workshop that i could nurglfy to make into a beast of nurgle?