At first, I mainly used a sleeping bag (not like a shark one or something that actually looks like a monster), but then I started using a futon in a fashion similiar to Reddmann's Chompps. Recently, I've been putting a couple of pillows (or couch mattresses) together to make a mouth and a blanket to use as a body. The problem is, however, is that these are all fairly lacking to terms of what I'm actually hoping to achieve. I've tried googling methods of how to make a custom one (especially of the plant, as I'm a big fan of plant vore, or maybe even a snake), but I haven't found much. I did find a bit on how Darkslade made his Weeblefeaster, and that gave me a couple of ideas on what I'd like to do, but I lack the proper know-how (such a step-by-step process) on how to actually make one.
Here is a small amount of some of the photos I managed to get in the past as a few examples of what I'm doing. Mind you, all my models are women.
Spoiler: show