You could buy two pads, if you can find a 2' x 10' pad, or one large 6' or 8' x 10' and cut it to fit....whichever suits your budget. Sometimes it costs less to get one larger pad and cut it down, then to order two smaller runner pads. Here's the type I've always used on my hardwood floors, and these have held up well. You can go a step higher in quality and get one that's felt backed, but I've never had any problems with the less expensive ones, unless the carpet is really light weight.

Here is a link that might be useful: carpet pads

Somewhere on the internet, there is a fabulous website that explains the various types of carpet pads and what they do. I wish I had saved the link. If I find it, I will post.

There are a number of different pads available.

The best for runners (IMO) is the Rubber Anchor brand non-slip pad. It is a solid sponge rubber. There is a new pad on the market that now has an open weave and is made of jute & rubber (just got my sample the other day) but I haven't tried it out yet.

If at all possible, it's always best to buy the pad from a dealer so they can cut if off the roll for you. The rubber anchor comes in a 32 inch width which would be ideal for you (also comes in other widths). It really is no more expensive to purchase from a dealer than purchasing online or at a home store.

I made a vid some time ago showing 3 different pads if it helps for you to see and hear the descriptions.

P.S. I am NOT selling anything here nor do I do any sales on the internet, just fwiw :-)

Here is a link that might be useful: 3 excellent rug pads

thank you so much! I knew I would get good info here. I am reading that buying a pad one inch smaller on each side is appropriate. Is this your experience, too?

Delta, yes 1 inch smaller is what I always cut pads.

I didn't "buy a pad" for my runner. I went to the carpet store and had one cut to measure.
Linda C