Thanks everyone for the sensible sounding advice.

I think I need to persist at this a little longer, then. I'll keep trying with the sling - will try to get the tummy-to-tummy position right, maybe with DH's help we can sort it out. If that still doesn't work for me the next thing I'll try is a wrap I've borrowed from my sister - I think it's a didymos, not certain.

It certainly is true that this stuff doesn't seem to come "automatically", or at least it certainly doesn't to me. Steep learning curve!