Some of the  current and most of the old sealants are unbreathable but there are a wide range of new sealants which incorporate nano technology which enables them to protect the stone without compromising its drying action. 

I get asked about this quite a bit and it is this simple; there are sealants which are so thin that they cover the inside of the stone of mortar with an incredibly thin layer which water doesn't like flowing over. It covers the inside of the pores NOT fill them. 

They can cause issues in some cases with weak salt laden stone but for applications like keeping Yorkstone clean, craic on. The sealants can trap salt behind them which them expands, stone like Millstone grit and Pennine Blue couldn't give less of a shit about that. Some pathetic Southern limestones will probably just fall to pieces as soon as you even think about it though. 

I would also suggest the considered use of Lithofin products. I've used them for years and their technical helpline isn't some idiot with a computer, those guys know their stuff. Or from a respected masonry conservation brand. As with most things you can generally tell by the price and availability. If you can nip down to the local industrial estate and buy it for buttons; its going to ruin masonry. If you have to use some weird poorly functioning website, pay a ridiculous sum and then wait weeks; it will probably be correct. Although Lithofin is reasonably priced and readily available... so the times they are a changing.