In my opinion bound armor uses up too much mana to be useful.
For example, let's assume you need 250 mana to kill of an enemy while using no armour. Using Light Armor will reduce your magic efficiency to 95% if you're proficient with it (Don't remember if that's above 25 or 50 in skill). This means that you while wearing light armor you will instead use 250/0.95 = 263 mana* (se below), which is an increase of 13 mana.
Now, if you cast the standard spell Bound Cuirass, which lasts for 60 seconds, you will need 15 mana at Conjuration skill of 100. Thus allready with just one piece of bound armor it hardly seems worth it.
Let's have a look at a case where your armor reduces your efficiency to 80%. 250 mana at full efficiency becomes 250/0.8 = 313 mana, which is an increase of 63 mana.
You cast your Bound Cuirass for 15 mana and think you've saved 48 mana. However, unless you're not wearing any helmet, shoes, grieves etc, your efficiency is still at 80%! So, either you will have to remove all other pieces of armor or replace them all with Bound Armour.
Now, if you continue to cast Bound Armour:
Boots: 5
Gauntlets: 4
Helmet: 5
Greaves: 9
Shield: 44
---------------
Total: 82 Mana (including 15 for the Cuirass)
Also, if the spells you were casting during combat used up 40 mana/spell, that's 8 spells in normal armour, 6 with full set of Bound Armour. Total spells cast with Bound Armour: 6 for armour, 6 offensive spells = 12 spells total. You're still better off without the Bound Armour.
If you want to stay at peek efficiency, I recommend getting shoes, pants, shirt and a hood. Those are all clothes and does not effect your combat efficiency. Then go enchant them with Shield. Using Grand Souls you will get 10% per piece for a total of 40 armour, which roughly equals a full set of Glass Armour. You could also go with Shock/Fire/Frost Shield instead. They give the same benefit as a normal shield plus the added elemental strength of the respective shield types. Grand Soul enchants give 9% for elemental shield thus giving a total of 36 armour.
However, another choice is to stick with normal armour (6 pieces as you can also use shield and gloves), enchant them all with +10 intelligence for a whopping 60 intelligence which gives you 120 mana...
*This calculation is somewhat simplified as the mana cost of spells is not increased. It is the actual effect that is decreased, like amount of damage done. As such, you might kill off certain enemies using the same number of spells, or you might need one or two additional spells to do the trick. Thus the actual mana spent could be 250 mana or something actually higher than 263 mana. Also, as far as I know the magic efficiency reduction only comes into play for quantitative spells like feather, healing and damage spells, not 'fixed effect' spells such as creature/armour summoning.
If you have trouble understanding any of what I wrote due to language problems, don't hesitate to ask and I'll try to clear things up
regards
Qizatch