This is something I've conjured up. Do with it as you please:
https://classic.wowhead.com/gear-planner/warlock/undead (100+ health libram on helmet/pants, seal of wyrnn if alliance)
As a 19 Warlock, you really won't need more than 1k mana. With any more than 1k mana, you won't ever need to use Life Tap (one of your most useful abilities). I personally think 19 Warlocks work best when they're geared for (almost) full spell damage, but if that's not your cup of tea, then I'd suggest a full stamina build.
Here's how I would do each build + talents:
Phase 3 Alliance Warlock Spell Damage Build
- 100 HP to Head/Leg not accounted in Gear Planner
- Change glove enchant to 20 Shadow Power during Phase 5
- Add fishing gear in Phase 4
Phase 3 Alliance Warlock Stamina Build
- 100 HP to Head/Leg not accounted in Gear Planner
- Change glove enchant to 20 Shadow Power during Phase 5
- Add fishing gear in Phase 4
As for talents, I highly recommend both 2/5 Suppression and 5/5 Improved Corruption. The first talent will hit cap your Affliction spells (Fear, Curse of Agony, Corruption) against level 19s (this does not affect their spell resistance from gear/racials). I'm surprised no one ever gets this talent.
The 5/5 Improved Corruption talent will allow you to cast Corruption on the move and really help your positioning.
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Switch those bracers for Mindthrust perhaps?
I feel like Mindthrust Bracers are one of the worst items for 19 twinking. Yes, +7 Intellect from bracers alone is nice, but if you're really having huge mana issues, you should be wearing some sort of Spirit staff with the 20 Spirit enchant out of combat. Stamina really is king at 19, so -5 Stamina is really just shooting yourself in the foot.