I used the size 0 kissaluvs with xs thirsties in the beginning. they worked great and were out of the way of the stump and clamp so didn't interfere at all. We're still using the size 0's at nearly three months too, still fit ok, but absorbency wise they are not lasting as long. excellent for containing nb poo though and very cute on a tiny bubba
ETA: just saw you q about boosters... I bought one kissaluv booster to go with each kissaluv. just used the one and I had to fold it in half to have it in the nappy.