My suggestion is Divine Soul Sorc 1, Paladin 6, Warlock (Hexblade/Pact Blade) 5, (in that order), race Scourge Aasimar. My reason for this is that your DM tells you that you will be fighting hordes of undead skeletons.
Stats (27 Point Buy)
Str: 13
Dex: 14
Con: 13 (+1; 14)
Wis: 11
Int: 8
Cha: 14 (+2; 16)
Paladin 4 takes +2 to Cha; Warlock 4 takes +2 to Cha; final Cha is 20
Stats (Standard Array)
Str: 13
Dex: 14
Con: 12 (+1; 13)
Wis: 10
Int: 8
Cha: 15 (+2; 17)
Paladin 4 takes +1 Cha, +1 Con; Warlock takes +2 to Cha; final Cha is 20, final Con is 14
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Going Divine Soul Sorc as Level 1 will give you Con Saves proficiency, as well as access to Cure wounds or Bless (you should likely be a Lawful Good character for this build, if that has any bearing). Also, Favored by the Gods can turn a little misfortune to your side once per Short Rest, which is good. What REALLY helps out is more cantrips and some spell slots.
Fighting undead means you will want a good source of undead damage, so Paladin is key here. Your Turn the Unholy Channel Divinity, as well as your double damage against Undead with Divine Smite, will be powerful tools here. Also, even Paladin numbers are great to make sure you don't miss out on any spell slots from MCing. And, of course, you get Extra Attack, all armor (I'd recommend going medium armor + shield, your best options for your Strength and Dex), all weapons, Lay on Hands for some insta-heal AND... the cherry on top, Aura of Protection. With max Charisma, this +5 to all Saves will feel great and any allies within 10 feet will love you.
Hexblade gives that sweet, sweet Charisma attack. In addition, you've got more cantrips, Pact Magic (2 3rd level slots per Short Rest) and Invocations. For those, I would recommend Agonizing Blast (Eldritch Blast obviously being a requirement to take for some ranged options), Eldrtich Smite (I'll talk about this next*), Improved Pact Weapon (unless your DM gives you magic weapons that make a +1 irrelevant, in which case I would grab Cloak of Flies, as this will give you auto 5 damage to any creature within 5 feet of you, which would help in dealing with weak hordes). Spell selection should include Hex and Shield (unless you got it with Sorcerer) here, anything else is debatable.
*Why Eldritch Smite? Since we already gain Divine Smite from Paladin, isn't this wasteful? Well, you may want to talk to your DM, but since there is no action cost to either of these abilities and no stated limit that they can't trigger off the same melee attack, you could Eldritch Smite (instant Prone) and Divine Smite (double undead damage) on the same hit. Which is great... but where it really comes into play is the Hexblade Curse. With a 19 Crit Threshold, it becomes much more likely to hit a Crit. If you do, suddenly you can use both of smites on one Crit. This means that, assuming an Undead target, you are doing 4d6 (Divine Smite) + 4d6 (Divine Smite Undead damage) + 4d6 (Divine Smite Crit) + 4d6 (Divine Smite Undead Crit) + 4d6 (Eldritch Smite) + 4d6 (Eldritch Smite Crit) = 24d6 (average of 84) extra damage (in addition to your normal weapon crit damage). Its quite the nova and, unlike other Warlocks who would Smite, you still have Paladin and Sorcerer spell slots to cast things like Shield or Hex with.
If your DM is not on board with the Eldritch Smite/Divine Smite stack, the above option is still on the table, just with 16d6 damage instead of 24d6. In that case, drop the Eldritch Smite Invocation and pick up one that suits your taste, possibly Maddening Hex, since it can deal area damage... but maybe not with Psychic damage? Monster Manual skeletons don't have any resistance or immunity to it, but your DM may be throwing crazy versions at you.
So... there you go. Lots of spells, lots of martial capability, great Saves, 18 AC, pretty damn decent health. You'll be max stats for both casting and attacking all in one, which will make you capable on both fronts.
You may not survive the uber encounter the DM is throwing at you, but you'll be able to recharge pretty effectively with a Short Rest and will be able to take quite a few folks down in the process, so have fun!