sounds like you're angling for single speed, not fixed gear, which makes me think of two options:

1. a flip-flop hub with a freewheel on each side, 1 or 2 teeth difference. front and rear caliper brakes. You should be able to adjust the brakes easily enough when you flip, if you keep the cogs pretty close.

2. a fabulous 2-speed coaster-brake kickback hub. these are a riot. you get two gears: "starting" and "cruising." And a coaster brake. You'd wanna run a front brake too.

Now, if you are thinking about running at least partially fixed gear, which you should, I'd say try option #1, with a freewheel on one side of the hub and a smaller track cog/lockring on the other side. you'd still want front+rear caliper brakes, but at least your rear hub will be a little lighter (freewheels weigh a ton!).

fyi, a "coaster/fixed" hub is a contradiction in terms, since by definition a fixed gear hub won't coast. There was a 2-speed fixed hub created by Bikesmith, and I understand it's still available, but, again, this doesnt sound like what you're after.

I'm gonna say it again a few times to get jimv's or schwinnbikelove's attention:
coaster brake coaster brake coaster brake

ok.