I use Dermol 500 lotion, it's OTC or on NHS prescription.
I use it for hand washing and showering, I never use normal soap or detergents.
Detergents make me itch like crazy, soap isn't as bad as shower gel if moisturised straight after, but you're best using a cream.
I cover myself with the cream, then wash it off in the shower.
My back was still getting itchy, so I switched to washing my hair separately in the basin. That way the shampoo and conditioner don't touch my back or legs and I think stay less itchy.
Yesterday some clothes washing detergent touched my hands and I scratched until it was raw red near my elbow, not even where it touched me, then this morning my other forearm was red raw when I woke up.
I'd taken two types of antihistimine as well!