I have stopped ironing sheets and duvet covers altogether, though I sometimes still iron pillowcases for guests. I don't find it makes any difference to comfort. The newest duvet cover I bought for our spare room king size has a dark blue William Morris pattern so TBH you can barely tell whether it's been ironed anyway!
Having said that, a Father Christmas duvet cover set I bought for Gdcs last year did feel very harsh and scratchy until I'd washed it at least twice. Admittedly it was very cheap, though.