Until you gain more CP and level Undaunted to gain higher stats it's safe to put 10-14 points into health and the rest in to magicka. Try to wear 5 Light 1 Medium 1 Heavy armor pieces and level undaunted skill by completing dungeons. There's a passive called Undaunted Mettle that gives you +1/2% max stats based on the types of armor equipped. You need 5 light to fully make use the passives from that armor type. Also spec the heavy armor passive Juggernaut that gives you 1/2% more health per heavy armor piece equipped. Don't use tri-glyphs as some suggested, since Hakeijo is pretty expensive. It's about 11K gold ATM on EU-PC, but an attribute point reset is only 3.2K at the altar in the alliance capitals. Once you level undaunted and gain more CP your stats will be higher so you will be able to shift all your attribute points in magicka and still have about 16-5.17.2 K health. Your resistance will also be higher due to having more CPs in the red constellations. So it's a matter of adapting your build as you progress.

you have a light armor skill that give you a huge damage shield. the more points you have in magicka, the bigger the shield.

relying on health seems wrong for a non-tank magicka character

For magicka builds there's also a bit of "fake health" they can use. The light armor shield skill, annulment, preferably morphed to harness magicka. It adds 10-12K and scales of your max magicka. That morph also recovers magicka when you are damaged by magic or elemental attacks.