I recently made 10 tutus for my granddaughters birthday,they live overseas, so didn’t know any sizes.
I made a separate waistband 3″ longer at one end (than the gathered tulle) then attached the layers of tulle (leaving the 3″ tail) folded over the waistband, tucked in the raw edges on the 3″ tail, then sewed velco onto the tail and corresponding velco onto the waistband, that way they can adjust for tubby or skinny tummies.
Then cut a long piece of ribbon (big enough to go around tutu and do a big bow at the back). I stitched this at centre front and then where I thought side seams would be (through all layers). When we sent them over we rolled them lengthwise and put them inside a pantyhose leg, this stopped them from getting crushed and reduced the bulk in the parcels, they didn’t weigh much but were very bulky.
Hope this makes sense. Good luck, if you need help with my ramblings just yell.