A P/J sounds great with both pickups blended, but I think a soloed J bridge pup sounds a bit weak. A P/MM (with the MM in the sweet spot right up close to the P) doesn't sound as good blended but it does give you a more usable soloed bridge pickup.
Options - add a coil split switch to the MM to give you just the south coil - this should sound close to the single coil J and perhaps blend better with the P. Especially if you use that funky Delano pickup that is half J and half MM. Or, what I would love to do, but would ideally need an unrouted body as a blank canvas - 70s position J + sweet spot MM + reverse P!