My potatoes always sprout, in dark bags, or in the fridge... I don't have a cellar - I do have a garage which will have a space in a cupboard. Would that work?
I don't use peat or sphagnum moss any more, as there's an issue over here with the depletion of bogs. Peat free compost is not as good with regard to water retention, but it's necessary.
This year's potato bags have much stronger growth than last year (I used growmore fertiliser), and the main crops are now flowering.

Penny