Can I buff my Atronachs in Skyrim?

In the vanilla game all conjuration summons have fixed stats and are unable to be buffed by your illusion magic*. Higher tier atronach spells will result in a slightly stronger atronach (i.e. fire->frost->storm) as well the elemental potency perk in the conjuration tree.

However, there are many many atronach mods available on the PC that you can use to increase their use. For example, Atronach Scaling levels them up to match the player level.

*Taking the master of minds illusion perk will allow your illusion spells to affect your summons. You are probably better off just getting our conjuration up instead and using higher level summons as it requires illusion at 90 to obtain. I've played a pure summoner mage before and I haven't found many things that can handle an endless stream of dremora lords, especially when they appear 2 at a time.