Mnnice -- sounds like you really love your bed! This might be the best route for you to go:
1. Buy a 99cent shower curtain for your guest bed or carpet depending on where the mood strikes you to labor. Make sure you open it up to air out well before you're due date. The smell of plastic is not very comforting and can cause nausea during labor.
2. Buy a vinyl mattress protector for your bed. It's like a pocket that your plain mattress goes into and gets zipped into. Then your mattress pad goes over the top and then your sheets and then your covers. The cost is from $15-40 depending on the size & quality that you want. Put this on your bed well in advance. It's great in case your water breaks, you throw up, you pee or have messy sex with chocolate (thought I'd make the conversation a little more enticing). Then, when you go into labor, if you feel like hanging out in bed, you just pull off your good sheets & mattress pad & put on some old ones. Also, it's a great thing to have when a newborn comes to your house. Even if you're not planning on cosleeping, the baby will probably be in your bed a little bit in the beginning. The vinyl cover will protect your mattress from any baby juice (ie spit, spit up, poop, pee, breast milk, etc). You can find these vinyl covers at most stores like Target, K-Mart, Wal-Mart, etc.
You never know what's going to work for you during labor. It's best to be prepared for different places you might decide to labor or push out the baby. The trick is to not spend an arm & a leg on things you may not use. Who knows, you may just like to push on your toilet. Talk about minimum mess!
Also, moonshine, I should say, most homebirths aren't messy. But, a bottle of Hydrogen Peroxide on hand is a good idea in case blood gets into the carpet. Chances are -- there won't be a spot! Lots of Chux pads, help protect things, too.
Best wishes to both of you!