Some .015 thick patches will be a good start to get the best out of your rifle.
The patchs must not only hold the ball and transmit the riflings rotation to it but they must also totally seal the hot powder gasses behind the ball.
The .010 thick patches you were using with your .530 balls make for a .550 diameter assembly.
While .550 sounds pretty big for a .540 diameter bore, the rifling in these guns ranges from .005 to .010 deep for most factory made guns.
If the bore is .540 diameter and you add in some .010 deep rifling on each side of the bore the diameter of the rifling grooves becomes .560.
That's why a .550 ball/patch diameter will not seal properly.
Going to a .015 thick patch the effective diameter of a patched .530 diameter ball becomes .560.
If your shooting one of the shallower grooved barrels like a Thompson Center or some CVA's with .005 deep rifling, that would work.
If your shooting a Lyman Plains Rifle with .010 deep rifling grooves even the .015 patch will be marginal.
That's one reason many of us use .018 thick patches.
As for the patch lube, any good lube will work.
Bore Butter is good, Mink Oil is good, even Ballistol seems to be good.
One of the best I've found is Stumpkillers Moose Juice, a mixture of water, alcohol, witch hazel, caster oil and some Murphys Oil Soap.
If your interested, look for it here:
http://www.muzzleloadingforum.com/fusionbb/showtopic.php?tid/203261/