Indoor potty training? Which type of artificial turf is best?

I slipped and fell on the ice during the recent weather & it's becoming more clear that I need a plan to deal with bad weather. Fortunately, I was well-padded by winter clothing, but I'm sore. And old enough to know it's not going to get easier.

My 20 lb Schnoodle is 5 and was really easy to house train, to the point that now, he won't go at all inside. I got him puppy pads hoping I could lure him to those, but nope, so he ended up spending the night in the bathroom, doors closed, with the pads and his bed. Never used them and no accident. He'll hold it for 18+ hours rather than go in a bad rain.

So, I'm going to buy some turf. He does use the artificial turf in the outside doggie area of my apartment building, so I'm thinking I'll take a piece of turf outside during better weather and train him to use it.

Any advice about the type or size or anything? He's not a big dog, but he likes to move around a bit before anything comes out the back end.

Edit: It can't be too large because I have to carry it to the outside pet area, and I will only use it occasionally. Thanks!