IMO Terry and Velour run similar in size (I wear the same size in both). You can usually find them on sale at Off Saks or Nordstrom rack. Often Saks and NM/BG will have them on sale online as well... hope this helps!
I have a few terry things
The tops and bottoms do not aka the juicy track suits
The terry cover ups because im a b-c cup I had to get a Small. when I usually wear a Petite in every thing else. I say if you have velour track suit in a small then get the terry track suit in small too.
nordstrom rack & loehmanns had lots of terry & velour tracksuits about a month ago but i don't think i saw any there today, except for one or two L/XL pants. saks off 5th had a wall full of juicy and seemed to have a pretty good selection in both colors & sizes. their prices are higher than nordstrom rack but are still good deals. i can't help you on sizing but i buy the kids size and the terry seems to stretch better & fit looser.