Because recasting is out of the question for me, if I were the producer (and this is the way I hope they will approach it), I would just let him stay at his true height (might be elevator shoes/ wedges, but no apple box), and put layers on him so he just looks lean, not very thin like he is irl (in that graveyard scene with Jeremiah his shoulder blades visible through his clothes was a bit distracting).
I don't think putting him in a pad suit (like Zachary Levi in Shazam, or maybe that wasn't a pad suit but it looked very much like a pad suit to me) would be a good idea because (1) it's unauthentic/ not genuine, because everyone knows David doesn't look like that (2) Gotham haters (and I swear haters who hate-watch seem outnumber the audience who actually enjoy the show) will just have more reason to laugh/ whine at the show and mock the actor.
And because of that I don't want the show to pretend he's a 6'2 bulky Batman either. I think there's little harm in making Batman a guy with average physical status (Gotham has done differently from the comic with regard to the background, origin stories, etc. of other characters, I don't think being different with regard to the height and build of an otherwise almost perfect Bruce Wayne is that important). In late season 3 Alfred said to Bruce something along the line of "And you plan to take on the man twice your size", and I want them to double it down in the last season, i.e. letting other characters commenting on his foes being twice/ thrice Bruce's size a couple of times, so no ones can accuse of the show of making the audience "pretend David is as bulky as comic book Batman".
And it's all fictional, so I don't really care that much about whether it's realistic anyway. Peggy Carter is shorter than Bruce and she battled men twice her size wearing a pencil skirt and high heels, so who cares.
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