Go to
http://www.simplicity.com/c-156-babies.aspx In the upper right click on "see all" & scroll down. Note: patterns are sized by weight/height....click on the dress then size chart. I saw 3 or 4 dresses/matching panties that may be what you are looking for. The patterns don't say they are for stretch fabrics, but I would think you could use them anyway. You may need to omit the seams on the pattern to make the dress fit snugger due to the stretch. It would depend on the direction you cut the fabric/i.e. direction of stretch of fabric. I would use a serger to do the seams & if you don't have a serger then pin pin pin, as velveteen/velvets are very slippery & will walk like crazy, even with a walking foot. I would also not use any double layers of velvet or velveteen, as it makes it a tad thick & seams way to bulky. I'd line it with a nice light weight lining fabric where lining or double layers are called for.
In place of a lot of gathers at the waist or the bottom of bodice I'd do a few wide pleats to keep some fullness, starting at side seam going in opposite directions & meeting in the middle front with a sort of "V".
Good luck.