Every company I have worked for, has had a dedicated set of life jackets per aircraft, and then some spares. But it ha always been in a temperate climate (Europe/North Sea).
We wore survival suits a lot of the time, so the sweat does not reach the LJ, and on hot days a flight suit which kept it bearable.
I understand that changeing from your personal safety equipment to a shared piece of equipment is uncomfortable by itself. For the hygene part the solution of 2 sets per aircraft, with time to clean and dry the worn sets, seems adequate.
Really personal equipment like clothing, helmets and gloves are different. They are in direct contact with skin.
We don't change the seats where the sweaty bums have sat all day, between shifts either, do we? Where do you draw the line? I think it is where you can find agreement with the employer. Make sure you get good life jackets that are adjustable, easily cleaned and safe.