Xfinity compatible modem (w/o router) that allows DHCP server to be turned off

I'm looking for a modem that works with comcast (that I don't have to rent from them) that will allow me to set static IP's for a couple of pieces of hardware upstream of the wireless router and let that router assign dynamic IP's to everything downstream from it. Basically I just want to be able to shut off the DHCP server function on the modem. I have business service from comcast so they'll assign static IP's for me, but only if I use their modem. Any help will be greatly appreciated, thank you.