Wads as fillers are relatively expensive, but if you insist you should choose a wad nominal .454" * and thick enough that when the ball or bullet is seated with moderate to firm ramming pressure it sits just below the face of the cylinder - as far forwards as possible while allowing the cylinder to rotate. For a ball that would be quite a thick wad. Sainsbury's semolina is much cheaper as a filler and allows adjustment of the BP charge without needing to procure lots of different thickness wads.

* (ROA is nominally .454" at the chamber mouth and a .457" ball gets shaved during ramming for a good fit - a .454 ball will also be OK but most find better accuracy with the .457 or even .460 ball)

The need to also use lube is somewhat controversial. MLAIC and MLAGB rules mandate the use of some kind of grease over the ball/bullet, allegedly to reduce the chances of a chain fire. It's function in the prevention of chain fire is disputed by many. Note that nearly all bullets, both modern and those intended for use with nitro, have some provision for lubrication by the addition of one or more cannelures, and in BP rifles and nitro cartridges, this cannot be for the prevention of chain fire. Lube also has the effect of reducing friction between the barrel and projectile, and in BP guns greatly reduces the build up of fouling residue in the bore. A lubed wad might serve the latter two purposes, but does not satisfy MLAIC or MLAGB, however this might not be important to you. Various concoctions are in regular use as a lube, assorted brands and types of mineral grease, the hallowed beeswax and tallow mixture, and many others, or simply E45 cream. Lube for a wad probably needs to be relatively thin in consistency to allow some absorption into the wad and here the world is your oyster - many favour wintergreen oil but I don't use wads so have nothing to offer on this matter.