FormerlyHemlock
Hero
Half-Elf Monk (4 elements) - Besides occasionally stunning (but giants have good CON saves) the one that needs the most help. Lots of attacks but only ok bonus to hit and usually single-digit damage. Also melee but with the lowest AC. And if dodges with ki that removes the extra attacks and uses up a ki that could be a chance to stun.
If I die and replace the character we would be losing my archer, who's the only other real damage dealer. I'd like some way to boost up the monk to fill that position, without it being something that makes the most sense to help out the paladin if it's only going to help one (like Haste).
I'd suggest adding some physical crowd control. Since you're going up against giants, it's probably more effective to do this via spells than physical combat, which means you want a spellcaster. A Sorcerer throwing Careful Web will help that monk out quite a bit. (Many giants have weak Dex saves.) The paladin will benefit too to an extent, but since he's spell-slot-limited with his smites, the monk will benefit relatively more. Try an Alert human wild sorcerer 7 in order to maximize (1) your chances of going before the giants with your Web spell, and (2) the chances of the giants failing their saving throws.
Just to be explicit about it: the benefit of Careful Web is that it creates a zone in which PCs can move freely, but giants have to make a Dex save every round or become restrained, which drops their speed to zero and causes them disadvantage on attacks (and advantage to attackers) until they burn an action trying to get unstuck. (Too bad the Bard's not a Lore Bard or he could use Cutting Words to make it even harder to get unstuck.) Doesn't prevent the enemy from throwing rocks of course.
Other useful options can include Careful Confusion, Careful Stinking Cloud, Careful Hypnotic Pattern, and Careful Fear. You can also have some fun with Phantasmal Force against giants, e.g. "summoning" an air elemental for one of the giants to fight before ducking back behind cover yourself, although that helps the whole party as much as the monk. Plus there is the good old Polymorph-the-Monk-into-a-gigantic-beast trick, which again works better on the monk than the paladin because the monk's baseline effectiveness is currently lower.
You can take Inspiring Leader and/or Healer feats to buff the party even further.