Just so you are aware, a Shadow Sorcerer is a terrific thematic and mechanical addition to the warlock/sorcerer stable. At level 3, the Shadow Sorcerer gets the Darkness spell for free. In other words, it does not count against your Spells Known list. In addition, when cast using Sorcery Points (2), you not only have darkness but you can see in it. What this combo does is free up a spell slot and an eldritch invocation. Two Sorcery points is what a first level spell slot cost and a third level Sorcerer has 4 first level slots along with 3 Sorcery Points to start out with. It means Darkness may come on a bit later but , imo, the savings are well worth it.

Thematically, both Hexblades and Shadow Sorcerers have an intimate connection with the Shadowfell, which allows lots of room for RP and removes many of the convoluted backstories of how these 2 disparate classes can meld in one individual.