I wash all my down comforters (ikea) every other month. The newest one is about 8 years old. What One&Done posted is exactly how I do it. Because they shrink so much when wet, even the kings go in our home washer super easy. Well, IN takes some shoving, but once they're wet, no worries.
The only thing to be REALLY sure of is that they are TOTALLY dry. MUST use tennisballs (they break apart the feather clumps). And, as a rule of thumb, when you think it's dry... put it back in for 3-4 more hours. When totally dry it will practically be bursting at the seams puffy and when you squish it, it immediately pops back up instead of staying back down. If they DON'T get totally dry, they can grow a kind of almost odorless (actually, it smells a LITTLE like urine) mold that is VERY bad for lungs.
If the bed is too big for your home machine, the laundry mat is a good alternative, since their machines are WAY bigger... but that's spendy.
Option 1.5 is to soak the beejeebers out of it in the bath to get is "small" so it WILL fit in your home machine, or to wash it in your tub, and then dry it at the laundrymat.
Option 3 (1=home, 2=laundrymat) is "Kid'n'Pets" or "Nature's Miracle" sold at pet stores or QFC. The same enzymatic cleaner that you use on urine, poo, vomit on carpets/ furniture. It will totally break down the uric acids and biologicals. I just can't stand the smell.
And for NEXT time (or when cash becomes available)... check out SleepCountryUSA. They have mattress covers that are waterproof AND breatheable (you can stick your face into it and breathe right through it). On the desk in all their stores they have a lttle glass jar with blue or colored liquid and a square of it over the top. Doesn't let ANY of the liquid out, but you can blow bubbles through it if you like. Not plastic, doesn't rip, isn't noisy, doesn't make you sweat/isn't hot nor retains body heat. Has a super short kind of terrycloth weave on oneside and the cellulose stuff on the bottom (terrycloth side goes towards you/your sheets). We have them on all of our beds, and I can guaranteed from personal experience... they work GREAT and last forever. They are NOT cheap, unfortunately. I bought ours during one of their sales, and they were still $50 each. I think they're about $100 normally.