Ah, good ol' build a better mousetrap time.

Here's a version I don't think has been proposed before:

True Strike
Casting Time: 1 bonus action
(No concentration)

If you make an attack this turn and miss, the next attack you make before the end of your next turn may be made with advantage.



If you have it, there's basically no reason to ever not use it, but I don't think it's broken, even if you combine it with Great Weapon Master and War Caster (which is a combination that I don't think anyone would normally take). No concentration roadblock, and no interfering with action economy, other than perhaps duel wielding. (Since you have to cast it before the attack that missed, you have to choose whether to use the spell or use the offhand attack, but can't only use the spell when you miss.)

You also can't guarantee it will affect a specific attack, which avoids a certain amount of cheesing (though not all). Mainly, it's not just a +4 to your next attack, affecting all of your attacks, meaning it's just a free +4 proficiency or whatever. Rather, the above makes the spell less impactful the stronger you get, but more useful during those early levels where you're missing all the time.