For over a decade I have been using the tiny switches recovered from discarded computer mice as keys. They are easy to obtain, free, and very reliable. Most seem to be of the same design and dimensions, some easy to disassemble and put back together. The mice, usually found free at yard sales or computer repair shops, are simple to open. The switches are through-hole design and leave enough pin length to fold over and solder surface-mount style from the side. Most are Single Pole Double Throw configuration.
The single paddle key was made from a scrap of printed circuit board, the smallest hinge that I could find in the junk box, and two switches. I remember that Heathkit once marketed a single paddle keyer that used a couple of full sized microswitches the same way. I used four magnets from old electric toothbrush heads on the underside of the main board to keep it stable. I was surprised by how nicely this key works. Several others expressed amazement at the feel. The trick is careful positioning of the switches before gluing and soldering.
For a portable stand-alone straight key I use cords salvaged from an old ear plug or from half of a Dollar Store 6' 3.5mm stereo jumper cable. Just solder the appropriate conductors to the normally-open contact pins and fold the remaining pin over the cable for cable tension support. If you want to ruggedize the key put a glob of epoxy putty over the connections. I have used both configurations for several years without a problem.To use this diminutive marvel just pinch it betwixt thumb and index finger with the cable directed back toward your palm, find a firm surface like a rock, log, a table, or (if you have one) the thumbnail on your other hand. A bit backwards from pounding on the key. Instead, you use the key to pound with. With a little practice I can squeeze out a pretty decent 18 W.P.M.
Since the switch has a Normally Closed contact as well, you can put this to use in an on-board key situation to move the local oscillator frequency when not transmitting. This offset of several hundred Hertz will let you use a non-BFO shortwave receiver for reception or you can use it with a direct conversion receiver right on your project. I used this on several Pixie-type rigs to great success.Below is a photograph of my Gigantron 7000 40 meter transmitter. Lots of room left for goodies even with the key as part of the module.
I would suggest keeping the key on the edge of the board since you cannot be tapping the whole rig on the table and fingers seem pretty big at that point. You will be amazed how easily you can send with just the fingertip. I have tried gluing buttons and levers to the switch but I can't improve on the bare switch enough to make it worthwhile. If you can, pass your experience along.