My Altmer pure mage is lv. 42, with almost all of my magic skills maxed, except Restoration and Illusion (but im not using Illusion). However, I really like this character, and I don't want to make anything Legendary. What would be a good transition for a pure mage to become, a spellsword perhaps? But it would be hard to get my one-handed up, and my Light Armor skill is way too low to sustain any damage at my current level.

Decisions, decisions.

SkyRe-Skyrim Redone.

I'm on Xbox

Enchants and Potions will help you use your low skills. Increasing damage output of your sword and effective armour rating. I'd suggest doing this until they're at a useful level.
Or you could take out all but one enemy, and go toe to toe with them for the practice.

Use magic to shield you, or use it as armour whilst you train your one-handed skill.

Smithing ~ use transmute and then smith gold jewlery, smithing levels up fast

Alchemy ~ Giant's toe + Blue mountain flower + Blue Butterfly wing = One big chunk of XP and coin

Perhaps train with a trainer in light armor and one handed. Just enough to put a few perk points into those skill trees.

This. if you are in your 40s then you should have a good chunk of money. Investing in a trainer or 2 will probly be your best bet.