Sealskins are merino on the inside anyway aren’t they? I had limited success with them, mainly because I’ve got big feet and slim ankles making them quite a loose fit, water just goes in through the top of them then stays there.
I was doing Reed Chillcheaters over any old thin / wicking sock last winter, mainly because I don’t have any winter shoes / overshoes and the chill cheaters are good at shielding the draft that comes through summer shoes. They are longer, tighter, stretchier than sealskins. Wind and water tight but not really breathable. You can keep the rain out but have to accept you’ll keep a lot of the sweat in so you need a good thin sock inside that doesn’t react too badly to damp. I found good old fashioned rayon / viscose socks (labelled as new fashioned Bamboo Technology) worked quite well under them. Cheap football socks did too and are similar in length to the chill cheaters.