Dear Anna the primatologist suggested a Velcro jumper for the baby to stick on, so here is a design, with the addition of little loop-holds for the baby to grip with her hands and feet.
Apparently part of our evolution was to do with hairlessness and being able to leave the baby down as it has nothing to hold onto. Hairy primates have an infant that attaches itself permanently for several years, and it is said that this means the mother can’t have another baby within this time. I don’t quite follow the logic but perhaps I ought to read up about it properly instead of spouting hearsay. Then it might make more sense. But it does seem that having to carry baby is more problematic than a baby that can hold on by itself.