This looks great - I think the solution with the red star was a good one, you can remove it for washing. I wondered about using the overlocket on the jersey fabric - did it work well? Now, I am wondering what will happen to the leftover pieces of the grey top ... :D
Thank you @shanibeer. The overlocker is perfect for this job : it neatens and leaves no bulk. Unfortunately I sort of lack the skill to sew in the round confidently :D. I'm really good at sewing in the round in a normal sewing machine though (that's a long story...).
My sister-in-law instructed me to cut a snip near the start of the sewing to ease the fabric into the machine but that made me a bit worried; it worked though; she's a genius and my brother is lucky to have her.