D&D 5E Player wants to be a Death Knight but will use official rules: Build Help

[Paul Farquhar]

The D&D Deathknight predates the WoW Deathknight (1st edition Fiend Folio), and never focused on frost-based magic. Did always have Fireball though.

Aside from the Oathbreaker Paladin in the DMG, there is The Undead warlock in VGR (with pact of the blade). Also in VGR is the Dampyr lineage to make the character a bit more undead.