Not last Christmas but the one before Mia had a long-sleeved Christmas vest (the sort that has poppers underneath, I think it's called a onesie in America) that I really liked. Last year I tried to cut the poppers off and hem it to make a t-shirt as Mia had grown and the crotch was a bit short.
But I didn't know you needed a ball point needle for jersey fabric! So I made a right pig's ear of it.
Actually, this is a good example of what I have learnt in a year. I dug it out of the scrap bag and used a ball point needle and a zigzag stitch to make it into a little decorative cushion. It's stuffed with toy filling.