Hi Lanesville,
I think Sherwood tends to make better than average quality and value mattresses but to know the quality or value of any specific mattress always depends on knowing the details of all the layers in the mattress (including the foam density of any polyfoam or memory foam). It’s the job of a retailer to provide you with this information (or get it from the factory if they don’t have it) so that you don’t have to make a blind purchase with no way to know it’s real quality or value compared to other mattresses in a similar price range. I would ask them for the information and if you post it here I’d be happy to give you more meaningful feedback about that specific mattress.
I would avoid buying any topper where you haven’t tried the specific mattress/topper combination in person until you have had the chance to sleep on a new mattress for long enough to really know what type of topper to buy and the type of changes you need to make in the mattress itself based on your personal experience. You can see some topper guidelines that may help you choose the one that is best for you in post #2 here.
Buying a mattress is often difficult enough and introducing a second variable where there is no way to know or even guess how the combination will feel for you until you have some direct experience with a mattress can be even more difficult and I would deal with each choice one at a time. I would choose a topper (if you need one at all) based on your actual experience on the mattress and if you have the chance to choose just a mattress that doesn’t need a topper or doesn’t involve more “unknowns”, poor value, or “weak links” is usually an even more effective approach if it’s possible.
Phoenix