Before we settled here in Southern Scotland, we moved around a lot so I have grown veggies in many parts of the UK including Anglesey. For potatoes I have found that a variety which does well in one place may not succeed in another. For me, I used to grow Desiree for all the reasons you cite, but when we moved here it failed miserably! So it boils down (
) to experimentation. You might want to try a selection of varieties rather than growing just one kind. In past years I have grown 3 kinds at a time, one salad potato and two different general purpose ones, trying one new variety each year. This year we are concentrating on just the maincrop GP types. As our place used to be a potato farm I can only grow Blight Resistant varieties. The seed catalogues used to blare on about precise degrees of blight resistance but I've noticed they have gone a bit quiet about it now.
The two varieties I'm growing this year, sourced from JBA in Annan so good Scottish seed potatoes, both blight resistant, are Setanta and Carolus. Setanta is deep red, sturdy and a tiny bit 'agricultural' in texture here but it grows well, crops heavily and makes superb roasties and wedges, chips and mash. It also stores well. Carolus is my favourite, it has skin blotched with pink, is a bit more 'elite' in flavour but just as tough in the growing. It does all the things Setanta does too. Carolus is the one we run out of first!
For roasting I prefer a potato which softens a bit after a shoogle in the pan before adding to fat for roasting as it gives a lovely crispy texture - a trick learned from one of my sons
For slugs, when you plant the tubers, sprinkle a small amount of Organic slug pellets, which dissolve to iron which is naturally found in soils, around the tuber before covering it with soil. This helps but actually in spite of having probably more cold and wet than Wales does, we don't get too many slugs any more here.
For Blight, keep alert and cut off any dodgy looking leaves as soon as you see them. Slide them into a plastic sack so as not to spread the spores and dispose of them either by burning or in the bin. If the whole plant gets it, carefully cut off all the foliage, same deal with the sack and no spore spreading and leave the tubers in the ground for a while so any spores get washed away before digging them up and seeing what you've got. Use those straight away. The suggested varieties are both blight 'resistant' but that doesn't mean 'proof'.
I don't like the Sarpo brand - they really are agricultural to my taste, quite coarse.