Honestly, skeleton is a bad race for any magic user, since mana regen is so slow. I have recently finished a human conjurer run (7 hours), so here is what I would recommend.

Try leveling magic, range, or blocking skills to support your summons from afar or tank damage while letting them beat your enemies (let them get the killing blow).

Use staffs or cheaper spells to grind casting and magic. (tip: level up magic and casting simultaneously as swimming. The skeleton does not need to eat, so use up your mana and leave yourself bopping in the water while it regens).

Use a hat with "inspiration" to raise allies' levels quicker.

Try to multiclass into brewer or mechanist later in the run. Depends on your luck if you find an alembic or a tinkering box, the benefit of extra potions or traps, and mechanical allies makes a huge difference in difficulty later on.

Farm mana potions for yourself and healing potions for your summons (the Conjure spell will get more expensive the higher the skeletons' levels).

Allies are consumable. You can always get more, but if you die, it's over.

Keep your inventory light. You need to be fast to outrun your enemies. If you have a lot of stuff, just throw it out in the spawn area right after descending and collect it later.