My first suggestion is that you forget about adjusting the mainsheet while tacking. As a practical matter, the mainsail is self-tending when you tack. In a well-coordinated tack, the boom doesn't "smack." As the boat comes up to windward, the mainsail luffs, and then, as it falls off onto the opposite tack, the wind fills the mainsail gradually. When you're singlehanding a sailboat, you have to think like an expert in time and motion study. In other words, you have to eliminate every unnecessary motion, and accomplish everything as efficiently as possible, because you only have two hands, and, ideally, you need three or four.
Secondly, don't make any "fine trim" adjustments while you're tacking. You'll have plenty of time to make all those adjustments after the sails are filled and the boat is on it's new course. The essential actions are to (1) put 2-3 wraps on the lazy jibsheet and take up all the slack in the
line, (usually 2 is best. After the tack is complete, you might want to put a 3rd or 4th wrap on the
winch) (2) release the working
jib sheet, (3) steer the boat through the tack, (with practice, you can tiller-steer the boat with a knee, or you can
wheel-steer it, using the
wheel brake to hold it momentarily) (4) watch the
jib, and, as the
jib crosses the eye of the wind, start hauling in the jibsheet, and bring it in as fast as you can, (the more you can pull in by hand, the less you have to crank in under load, using the
winch handle.) (5)
cleat the jibsheet, and (6) make fine trim adjustments.