If you have a local fabricland or Marshalls they have lots of 4 way stretch fabric. Ask if the store has any swimwear fabric (even though you can't really make swim suits out of it because it would need lining and need chlorine safe fabric) but they usually refer to it as swimwear or active wear. You will need elastic for sure to put in the legs (don't put in the the arm and neck holes even if it says because it makes in uncomfortable). And don't forget the lining for the crotch area.
If your having trouble finding fabric look at:
Spandex World Inc. spandex fabric, lycra stretch fabric
They have tons of fabric and even have a clearance section and you can get a yard for 2 dollars!! And they have a seperate section for velvet.
If you are ordering just lycra fabric, go to printed spandex and after you choose one make sure that the fabric weight is 6 Oz/Sq Yard, 170 G/Sq Meter, 303 G/Yard (this is the typical weight and I find it the most comfortable for lycra, and the stretch direction in 4 way.
I have used the Jalie pattern, but don't usually because they are a lot more work and fit very skin tight (so make a size bigger if the fabric is super stretchy)
I usually use a Kwik Sew pattern for a regular leo.
For the elastic in the leg, measure the elastic on the leg of the user to make sure it's not too loose or too tight.
Good Luck making a suit! My mom makes almost all of mine now, because they fit perfectly and I can have a slit in the back so it can breathe. I even got one with the transformers autobot logo sewn onto the front!
Have fun, just let me know if you have any questions!