Recommendations please

DS is sensitive to soaps. I've started using cloth lately & am just using terry flats atm.

Last night I noticed a rash at the bottom of his back & I'm pretty sure its coz I'm just using a cheap powder from Aldi.

So should I try one for sensitive skin? Do they work? Or is there a particular brand that might be better?

Something I can use on my MCNs too when I get them would be handy.

Can you use vinegar on terry's? I use it on towels?