Well, if you're going for a "Dark" theme, then Paladin is probably not the best choice - Even with the Oathbreaker subclass much of the overall class is very much Light theme (With the primary feature being Divine Smite which is quite literally smacking things with light)
Druid/Warlock could work with a "Dark" theme.
Something like 7 Circle of the Spore Druid/5 Great Old One Warlock could work well (Fiend Warlock is also good)
Warlock provides Pact of the Blade to enable weapon usage with Charisma and a second attack (At level 5 with Deepened Pact), you also get Eldritch Blast, Hex, Arms of Hadar and Hunger of Hadar for potent (And dark themed) spells.
GoO vs Fiend is an choice. GoO provides AoE frighten when you crit and access to Tasha's Hideous Laughter and Slow. Fiend provides a small amount of Temporary Health on kill (It won't stack with Symbiotic Entity but can refresh it if it's lower) and provides access to Command and Fireball.
Spore Druid gives you Symbiotic Entity to provide extra Necrotic damage to your attacks and eventually you can start summoning zombies (Both with Animate Dead and Fungal Infestation).
For leveling, I'd suggest Druid 2 to get Circle of Spores, then Warlock 5 to get your Deepened Pact. Then finish off with the remaining levels of Druid. Prioritize Charisma over Wisdom as most of your attacks will be using Charisma.
On a side note: Paladin/Warlock can be a very powerful melee class if you don't mind losing out on the Druid aspect of the overall build (And can put up with Divine Smiting everything as a "Dark Knight")
7 Oathbreaker Paladin/5 Fiend Warlock is pretty good.
Warlock again gives the Charisma for weapons and extra attack.
While Paladin also naturally gets an extra attack (So you get 3 attacks per standard action just like a Fighter because Pact of the Blade stacks with normal extra attacks) and Aura of Hate provides your Charisma modifier as damage to your melee weapons (ON TOP of what it would already get from Pact of the Blade making it scale of Charisma base. Meaning you end up with 2x your Chr mod as damage for your melee attacks)
Similar leveling strategy as before, 2 Paladin to get Divine Smite then 5 Warlock then the rest in Paladin. Just stack Charisma out the wazoo and beat everything up with many high damage weapon attacks and plenty of Divine Smites.