Oddly - I got asked a similar question on another forum today...
What I'd prefer is to do this in a large corner bath, I lie back in the bath whilst she soaps me up.
Then she gets some liquid soap - the stuff for 'senstitive parts' (because it doesn't sting). She puts some on my cock & some on her tits. She then proceeds to rub my cock with her tits, one at a time & then between her tits.
She has to rub the underside of my helmet this way as it's the most sensitive part. Honestly - if you haven't had a large chested woman do this to you - you need to. It's fucking heavenly and wipes the floor with a regular tit wank.