I have a set of cream/denim striped couches that are several years old. They have awful sweat stains. How do remove these stains? Oh how I wish I could throw the couches into the washing machine!
You can use a diluted solution of hot water and oxy clean. Make sure the oxy clean is dissolved, dip a rag into it and rub your sweat stains out. I have kids and this takes just about anything out that is organic on my couches.
Have you tried a steam cleaner? I know you can rent them from grocery stores and such and they should have a hand held attachment for use on surfaces other than floors. I understand they rent for less than $20 which is a cheaper alternative to buying new couches or slipcovers.
I've cleaned my upholstery for years using good old dry Tide detergent. I put about 3/4 cup dry Tide into a deep mixing bowl. Pour about 2 or 3 cups of very hot water over the Tide. Let it dissolve for several minutes. Take your electric mixer and beat the mixture until you get lots of thick foam that stands in peaks. Take a wet washcloth you've wrung out (don't want it dripping wet!) and apply the "foam" to the dirty areas and scrub it around. At times I've then scrubbed with a soft scrub brush too.....it depends on the fabric. Then dip another clean washcloth into clean warm water, wring it out and wipe away the foam and dirt. Keep rinsing the washcloth and wipe the area numerous times. Don't soak the upholstery either during scrubbing or rinsing. Let it dry throughly........maybe a day or two......then run your vacuum over it to pull out any leftover residue. I have a recliner I've cleaned this way numerous times, over the past 20 years, and it still looks nice!
I use a tea tree oil soap scrub. Then I febreeze the heck out of it. If you can move the item into the sun for a time that is helpful too as the sun rays will also help kill bacteria which cause the odor.