In general, a cyclocross bike will have more aggressive (racey) geometry than a bike marketed as a gravel bike. Steeper angles, lower head tube, longer reach, etc... Cyclocross bikes also tend to have less provisions for mounting fenders and racks. But it seems like most come with two watter bottle mounts these days. Cross bikes also tend to have a wide open front triangle to allow/ease shouldering (and some will have a shaped top tube for this as well)
Gravel bikes tend to have more tire clearance and a more "endurance" oriented geometry as well as provisions for fenders and racks.
For what the OP wants, I think a gravel bike may be a better fit than a cyclocross bike. If nothing else because it will allow for bigger tires which are more comfortable.
I would also suggest considering a hardtail mountain bike. It will likely have a riding position more similar to what the OP is used to on the townie. And should also be more comfortable on unpaved trails.