There's a few different things you can do.
One obvious decision is for the whole party to take flying races so you can fly out of reach, meaning that way fewer enemies will be able to damage you.
Another option is to use stealth to get the surprise round, as going first is very valuable for a wizard.
At 1st level you'll struggle the most, but if you make sure to fight at range, choose favorable terrain, always be cautious, take Shield just in case, use illusions to redirect enemies, and use Sleep on larger groups, you should be fine. But even at higher levels remember that the day you don't prepare yourselves every way you can will be the day your party bites the dust.
At level 2, a Bladesinger in the party will definitely make you more comfortable, but as soon as you hit level 3 and get 2nd level spells such as Web or Phantasmal Force, you'll have enough area control spells to stall and drain your enemy of hit points from safety.
Starting at level 5, you're basically set. In most situations, a single dedicated necromancer will be able to provide more defense and single-target damage than two fighters of equal level(or three and more from level 6 and beyond) using skeletons from Animate Dead. But in case positioning in tight spaces, enemies with big AOE attacks and resistance/immunity to nonmagical attacks become problems for the skeleton army, having a conjurer with spells like Summon Undead or Conjure Elemental will be a good backup option. With those more than fulfilling the need for martials, the rest of the party can focus on area control, debuffs, AOE damage, and utility.
So basically, be sneaky and play it safe by stalling enemies with area control until level 5, and then do the same thing except from behind a horde of dozens of skeletons.
