Thanks for the recommendations. Dc and I have had a browse and we've ordered a hairy Tangle, a couple of squidgy hairy things, a mesh tubey-springy thing, and some hair-bobbles that are basically an endless coiled coil. Hopefully we've got sensory-seeking, finger-twiddling and tight squeezing all covered.
Don't know if it would fit the bill, but I have a little rubber diplodocus which is an amazing fiddle toy. I used to carry a pen around all the time at work, but the diplo is much better. Sadly looks like you have to by a set- but the red one is good too and spares always handy!