A double room normally means two twins (a triple means three twins...). In many hotels (usually in Paradors as well), you can request "cama de matrimonio" which is the traditional double/queen bed. These types of beds are usually scarce if available at all.

If the "share the bed" experience is vital to your travel, you'll just need to be a little more selective in your hotel choices (or bring two sleeping bags and zip 'em together on the floor...).