what platform are you on I can help you with some builds in game.

OK im PC so will just post some info and builds I found work for me.

I found with my Mag DK there are options but I found chasing the sustain to hinder my damage, suvivability and play style and have accepted that heavy attacks are going to be the sole sustain for all my builds.I also find sturdy to be much better than impen on Mag DK. I usually run resto with light armor and destro with heavy for 2 reasons. 1. Sustain (since heavy attacks are the sustain you will need either the bonus for heavy aromor resource return or the bonus from resto in order to sustain mag) 2.Spell pen (alot of ppl don't seem to realize how important penetration is to damage so running elemental drain will also help with mag regen and make up the difference in pen from being in heavy armor)

If your having trouble getting used to low sustain its best to start off with heavy armor and resto back bar. The DPS is a bit lower due to the penetration loss but its still very doable. For this I would run heavy innate axiom for chest, legs, gloves, shoes with light innate axiom belt. Valkin skoria heavy helm and med shoulders. Burning spellweave (or for ease of obtaining silks of sun although i think BSW is better) jewelry and weapons. SnB and resto back bar. Now in heavy you could run all impen since no CP or all sturdy since no CP or a mix of both, that will depend on play style. with nirn on your 1h. All Magica enchants. for Light armor i like to run all sturdy since its virtually perma blocking.

For skills i use the following:

SnB bar: whip, fossilize, embers, talons, flames of oblivion. Leap

Destro back bar: ele drain, degeneration, coag blood, dragon fire scale, volatile armor. Meteor

Resto back bar: engulfing flames, degeneration, healing ward, dragon fire scale, volatile armor. Resto Ult

Do yourself a favor and no matter what build you run use the Lover mundus.

If you want a pretty tanky LA build with extremely high DPS I run.

BSW, Silks of Sun and Valkin Skoria all sturdy since Mag dk is great for block casting and block mitigates so much damage that even in light armor you are tanky as hell as long as you sustain block. I personally feel impen is absolutely wrong for LA DK.

I would ditch the blood spawn and go Valk. BS is a great set but i feel much better suited to stam DK although its probably the second best Mag DK monster set in my opinion.

A few tips on Mag DK.

-Use you CC's constantly. This may frustrate other players but its the key to a good mag DK. fossilize every time its up. Talons provides huge synergy damage and can be use every 2 sec.

-Use your CC to your advantage. Once you CC a player while doing damage shift yourself behind them. This is very important. if you stand in front they have no reason to break the root from fossilize. thus not wasting thier stam and you getting hit. Also most attacks cannot hit you if you are behind a player. So CC and shift behind.

-Use your leap as not only an execute but mobility and CC break for roots or bad situations. CC'ed in a crap ton of AoE with no stam and looking like death with a leap up.... use it and get out. Leap to someone on the outside of a fight.

-Use your CC to gain back your resources. fossilize and heavy attack while shifting behind a player. Either on SnB or Back bar depending on resources needed.

-Pressure is key to Mag DK. so well timed HA's and constant dot pressure while maintaining enough resources to bust once they are below 50% health. Don't go full ham non stop. keep pressure and maintain damage then burst once you have the opportunity.

I could go on for a year but that some things I feel may help you and others may have something that fits your play style better but this has worked for me.