That's why I'm very happy with these monsters now available on DMs Guild. If they turn out to be well designed, they will fill a much needed niche for me. The D&D Denizens and D&D Citizens offer at least somewhat higher CR humanoid foes. The Monster Mausoleum offers higher (mid-levels) CR undead.
Here is another product I bought that is Pay What You Want.
Monster Expansion by "Scottomir" Metzger, tentatively 5 out of 5 stars.
(Tentatively because again, I will only truly know how well designed the monsters are and how accurate the challenge ratings are when I use them in play).
This has a variety of more powerful versions of beasts such as a great cave bear or greater tiger with higher CRs, and also a couple more powerful versions of each, kobolds, goblins, hobgoblins, orcs and trolls, and a couple more powerful versions of undead (wight king and dread wraith). The trolls include some interesting versions, not just more powerful, including the cave troll, stone troll, forest troll and mountain troll.