I need a little help with simulating.

[Z_lastname]

I may be able to help! Do you have any vests, or stretchy T-shirts that you aren't using? If so, this could help.
My method is I wear a vest and a stretchy T-shirt on my top half as usual. Then, I take another vest (or a stretchy shirt with the sleeves cut off) and I put my legs through the arm holes, so the head hole of the shirt is over my crotch area. I first put whatever I'm using to simulate my belly under the vest on my top half, then I pull the vest on my lower half over it, and then the T-shirt. It tends to prevent any lumps and bumps.

Try the 36 inch ball and deflate it slightly. Make it so that when you put it on, the side against your belly will be flat and the side facing out is taut and round like a baby bump.

If you want to go for more realism in the belly department, get a funnel. It is difficult, but by squeezing and moving the opening of the beach ball, you can fill it with some water, making it heavier. Also, the cold water in the ball feels great sloshing against your belly!

http://postimg.org/image/682o1o083/

http://postimg.org/image/5znz1maeb/

That's what my belly looks like with this method. I hope this helps you out!

Edit: Also, rather than buying a leotard, by a large size women's one piece swimsuit. Cheaper!