Are you using the Comcast-provided router and modem? If so, there are much better options out there to purchase, both in terms of speed and signal range. Yes it's an additional one time cost, but you'll end up saving money each month by not renting the hardware through Comcast.
For the router, look for something that has multiple internal antennae (or even external ones as well) and provides a nice range. You can find ones with great detailed reviews on Amazon (does anyone use Newegg anymore except to compare?). I purchased my current one about 30 months ago and I think that cost was recouped after 8 months of not renting.
Modem-wise, nothing super fancy needed. May want to look for one that has a few ethernet ports to run stuff in your office by direct cable for higher speeds and keep wireless traffic down.