fuindordm
Adventurer
I think it's OK for you to give grunts a minor bump to AC or saving throws. It will make a fight a little more difficult, but 5E gives you a lot of wiggle room in encounter difficulty vs. PC survival.
For solos/boss monsters, take a close look at the legendary monsters in the MM. I've tried a couple out in my game, and I like how they work. It's more important to give solos more actions than more AC or HP; and if you want a minor boss you can just let them act twice per turn, or give them a couple of bonus actions (to move or make a single weapon attack) that can be taken out of turn. The move action is particularly important since it helps them get out of situations where the whole party is in position to attack.
Cheers,
Ben
For solos/boss monsters, take a close look at the legendary monsters in the MM. I've tried a couple out in my game, and I like how they work. It's more important to give solos more actions than more AC or HP; and if you want a minor boss you can just let them act twice per turn, or give them a couple of bonus actions (to move or make a single weapon attack) that can be taken out of turn. The move action is particularly important since it helps them get out of situations where the whole party is in position to attack.
Cheers,
Ben