I'm not clued up on the Mothers range, so can't offer an opinion on how well the sealant you have will work; no harm trying it out mind! The P21S is a good wax and gives a cracking finish; it's just the durability that sucks, so many people reserve it purely for show car use. Other than the kit already linked, you could try this one also...

http://www.polishedbliss.co.uk/acata...-kit-kits.html

It will give you more colour pop, but less overall protection - I'd avoid paste wax products, as none of them will seal the finish as effectively as a polymer sealant (and you ideally need this benefit to help prevent the problems from coming back).