also, occasionally have it steam cleaned by a carpet/furniture steam cleaning company or rent a steam cleaner (that would have a hose attachment for steam cleaning soft furnishings).
i tend to do this seasonally (either have it professionally done or do it myself depending upon the time that i have. i do it on the day that i flip the mattress and adjust the level of warmth of the bedding. i typically have the bedding dry cleaned (organic) as well. quilts, wool blankets, and all that. i wash the sheets weekly, of course, but will wash them on that day too.
eg, at the end of winter, the heavy blankets are dry cleaned and put into a vacuum sealed "space bags" so that they stay clean until next winter. i then bring out the spring/summer/fall bedding (a light quilt and a lighter blanket for spring/fall), and make the bed with that.
so, the bed is dry by the end of the day, and then i make it and we go to sleep on a fresh, clean mattress.
seasonally works best for me. i'm just about to turn/steam our bed (next week) for this season. this weekend, i cleaned out our closets putting warm gear in the vacuum bags; pulling out cold weather clothes and putting them away.

i had the bedding cleaned last weekend (due to a fear of bed bugs, that we did not have), so we are good to go for the bed for next week.
