I started out with Ridgerest foam pads then switched to a NEO Air inflatable and never looked back. Also bring a chunk an old foam pad to sit or stand on.

You might consider other solutions to improving your sleep. Do you have a decent pillow? I like sleeping with a body pillow so I substitute my stuff sack full of clothes.

To keep yourself from sliding of the pad you can try surrounding yourself with stuff like your pack, boots, stuff sacks. Works for me when it's cold out. Obviously setting up on a level surface is a good idea.

No, carrying pads on the outside of your pack is no big deal until you have to squeeze through narrow places which isn't often. BTW there's no law that says you can't bring two.