I find I can get a ton of maltiness from 100% munich. If you want even more you can boil longer as well.
I recently mad a version of my standard porter with 90% Munich and will probably never make it any other way ever again. It really took it to a whole different level.
I also recently brewed a Porter with a much larger percentage of Munich than normal ( I think it was around 40%), and think it is fantastic! Really brought out some stone fruit flavors that I wasn't expecting.
So, I think adding some, or alot, of Munich for body would be a great idea for your single hop varieties. I also agree with another poster that 100% Thomas Fawcett Marris Otter works very well with a single variety.