Dropping into a higher gear, revs rising yet you are not going any quicker - sounds like a clutch overhaul is called for.
Buying OE clutch plates will mean years of good service, and if ridden with some mechanical sympathy, perhaps a lifetimes service!
We recommend that you give consideration to replacing all the plates and friction plates at the same time.
Don't forget to order new gaskets and seals at the same time, reusing the old ones is not recommended! Use the same gasket seal as the professionals: 08C70K0234M.