I confess to a preference for black powder but I shoot mostly older, original firearms, such as yours, that were originally used with BP, such as yours. You can clean the BP "gunk" from your smoothbore with 3-5 patches. That's just the way it is.
If you want the ultimate in simplicity just purchase a box of 2 1/2 brass hulls from one of several sources, Buffalo Arms is one, and you have a lifetime supply. You will need 11 ga. wads most likely and the only special tools you will need are a decapping punch, easily made from one of those little screwdrivers often given away as advertisement, and a dowel of large enough size to fit loosely in the hull. For seating the large pistol primers those hulls require the same dowel, something hard to place the primer on, (I use a scrap of our granite counter top), and a small hammer are all that's needed.
To load, the charge in drams is easily found out and a dram is 27.5 grains. Figure out your powder charge, dump it, (I do use Ffg, it patterns better in my guns), insert the hard over powder card, the felt cushion wad and I use another hard overpowder card on top of that. Dump your shot charge and insert over shot card. In the old days they used watergalss to hold the overshot card in place and it is still available. I have learned that Duco cement works just as good and is easier to come by and work with. Glue the overshot card in and you're done. If the load doesn't come up to the top of the hull, so what. Doesn't hurt a thing. For clean up I drop my hulls in a container of hot water, slosh them around a bit, repeat, let dry and throw in the tumbler just as you would your rifle or handgun cases.
A little experimenting may need to be done to find the load your double likes but that's part of the fun. It took me 3 loads for my German combination gun. If you have a sense of history I believe you will enjoy it. If not, find the nitro load, they are out there as others have shown.
