I think it would quite easy to take the Shadow Sorcerer and make it a Warlock's:
Eyes of the Dark
Starting at 1st level, you have darkvision with a range of 120 feet.
When you reach 3rd level in this class, you learn the darkness spell, which doesn't count against your number of warlock spells known. If you cast it with a spell slot from your Pact magic feature, you can see through the darkness created by the spell.
Strength of the Grave
Starting at 1st level, your existence in a twilight state between life and death makes you difficult to defeat. When damage reduces you to 0 hit points, you can make a Charisma saving throw (DC 5 + the damage taken). On a success, you instead drop to 1 hit point. You can't use this feature if you are reduced to 0 hit points by radiant damage or by a critical hit.
After the saving throw succeeds, you can't use this feature again until you finish a long rest.
Hound of Ill Omen
At 6th level, you gain the ability to call forth a howling creature of darkness to harass your foes. As a bonus action, you can summon a hound of ill omen to target one creature you can see within 120 feet of you. The hound uses the dire wolf's statistics (see the Monster Manual or appendix C in the Player's Handbook), with the following changes:
The hound is size Medium, not Large, and it counts as a monstrosity, not a beast.
It appears with a number of temporary hit points equal to half your warlock level.
It can move through other creatures and objects as if they were difficult terrain. The hound takes 5 force damage if it ends its turn inside an object.
At the start of its turn, the hound automatically knows its target's location. If the target was hidden, it is no longer hidden from the hound.
The hound appears in an unoccupied space of your choice within 30 feet of the target. Roll initiative for the hound. On its turn, it can move only toward its target by the most direct route, and it can use its action only to attack its target. The hound can make opportunity attacks, but only against its target. Additionally, while the hound is within 5 feet of the target, the target has disadvantage on saving throws against any spell you cast. The hound disappears if it is reduced to 0 hit points, if its target is reduced to 0 hit points, or after 5 minutes.
You can use this feature a number of time equal to your proficiency bonus before you must finish a long rest to use it again.
Shadow Walk
At 10th level, you gain the ability to step from one shadow into another. When you are in dim light or darkness, as a bonus action, you can magically teleport up to 120 feet to an unoccupied space you can see that is also in dim light or darkness.
Umbral Form
Starting at 14th level, you can, as a bonus action, magically transform yourself into a shadowy form. In this form, you have resistance to all damage except force and radiant damage, and you can move through other creatures and objects as if they were difficult terrain. You take 5 force damage if you end your turn inside an object.
You remain in this form for 1 minute. It ends early if you are incapacitated, if you die, or if you dismiss it as a bonus action.
When you use this feature, you must complete a long rest before you can use it again.
