We had to ditch synthetic fabrics completely - inners, booster, absorbent bits, the lot. I think we were using nothing but bamboo and wool by the time we'd finished with nappies. That did work well though, no rash. I was using Simply non-bio for washing, doing an extra rinse before the wash (didn't seem to need one after it) and line drying outside as much as possible.
Best cream we found (and it didn't seem to bother the nappies) was Earthbound Organics chickweed and calendula.