Kate isn't a Saint Bernard (she's a Leo) but we found a really neat bed, more like a cot actually. It supports the spine really well, sits about 4" off the ground, and has a really good warranty. She loves it (but) I bought it too small. I underestimated her growth! I'll be buying another one when she grows out of this one, but she zonks right out on it. She'll even lay on it instead of the couch with us (even with an invite)!!! She loves it a lot...
Here's a pic of her on it, my goodness she was so little when I took this!