HP and Monsters in D&D

Fifth Edition is the first version of D&D I've played, and I jumped into the deep end by DM'ing from the start.

While I don't think I've managed to weave the compelling narrative that you get with Critical Role or Acquisitions Incorporated: The C-Team (which I need to forgive myself for not quite getting as, even after a couple years I'm still basically new at this,) I think I've made the game pretty fun for the most part.

The only problem?

The party utterly slaughters my monsters.

I don't know exactly what it is, but I suspect it's that monsters don't really have enough health. I've also often had them fight one thing at a time, which seems to seriously handicap my ability to threaten them. When your paladin crits and tacks both a Thundering Smite and the standard Divine Smite on top of that, your monster is often going to just explode.

So I'm toying with ways to make combat more interesting.

One way is to really plan out encounters and ensure that there's environmental hazards.

Another is to just suck it up and use a lot more monsters against them. For example, they just fought an Orc Eye of Gruumsh (different name to fit the lore of my world) and an Orog, who, according to the DMG should have presented a reasonable threat to them, but they wound up obliterating the Eye and the Orog got a total of two hits in before he was killed.

I don't want to TPK the party based solely on my ability to tune encounters, but it's pretty clear that these things are not living long enough to be a real threat.

So my new "resolution" is as follows:

Always give monsters max HP (if they're like 8d10+24 then I'll give them 104 HP.)

Always make sure there are at least as many monsters as party members (using lower-level minions to draw the melee guys' attacks away and make the Wizard's AoE abilities more attractive.)

Strand them in difficult terrain circumstances, like collapsing bridges or rooms with lava jets and such.

We'll see if things get a bit more interesting.