Hi paisley,
There are much better “value” sources for a topper that use the same material (talalay) as the PLB topper but can be purchased in a range of firmness levels including slightly firmer (although still soft) that are in post #4 here.
If you let me know your city or zip I’d be happy to let you know of any options or possibilities in your area I’m aware of.
My previous replies include links to some of the members here who sell online and have some mattresses in your price range that would almost certainly last you as long or much longer than your 3 - 4 year criteria.
Phoenix