Don't do a plate carrier, even with an elastic cummerbund. Not only will it be uncomfortable but you'll look weird. Honestly, you can go with any chest rig you want (Eagle, TAG, First Spear, etc.) and just get an extender strap if it's too small on you which I'd find hard to do. It'll extend the strap that goes around your back so it'll buckle in and fit you.
Or, if you want, you can try H-harnesses or something like a Blackhawk LBV. Even a bigger guy on my team just wears a battle belt with a backpack. Holds plenty of mags and has nothing on his chest.