Definitely don't use boiling or even hot water, unless you want to super felt (and probably ruin) your wool.
Lukewarm water in a sink with a no rinse wool wash like Eucalan, let soak for a while (10-30 minutes, or so) maybe swish around a bit, then gently press the water out, roll in a towel to get excess water out and lay flat to dry. If you need to lanolize, just add a pea-sized (or so--per wooly, more or less) bit of lanolin, a couple of drops of wool wash and very hot water to a jar or other container you can put a lid on and shake, and shake until the lanolin is emulsified (the mixture will look milky). Then add your lanolin mixture to the wool already soaking in your sink, taking care to pour it all around and then swishing your woollies through. Let them soak, gently press water out, lay flat to dry.
Some felting is great in some kinds of soakers, but machine washing, vigorous rubbing and scrubbing, boiling water or too hot water, or tossing wet wool in the dryer usually mean felting to the point of ruin.
Avoid boiling water and rough handling because of felting. Felting might or might not ruin you covers - the will shrink (significantly) and lose elasticity. On the upside, they will be tighter and more waterproof. So they will most likely stop fitting, though I do have some covers with snaps that are purposefully made of felted wool that are just fantastic for nighttime.