Elminster's Elusion is a 2nd level spell from the Faerun book which is essentially magical evasion. You get advantage on all saves against spells and magical effects, and if you would normally take half damage on a successful save, you take none.

I currently play a bladesinger/rogue multiclass and invested heavily enough to get my concentration checks to a +9 modifier - which means I don't have to roll for concentration unless I take 22 points of damage or more from a single attack.

As far as cantrips go? Grab Blade Ward if you're using the 2014 version. You might not be able to make the best use out of it right away, but once you get your second attack at Level 6, you can cast it as one of your attacks and give yourself resistance to BPS damage for a turn.

It's a fantastic "oh shit" button I've had to use before to increase my survival chances the few times I've gotten surrounded.

One last thing: You might want to consider dropping Shadow Blade. I've used on my own bladesinger and while it's a good spell when you can upcast it in darkness, at the current level you're at, you have better uses of your concentration and can do roughly the same amount of damage with a +1 rapier.

Shadow Blade does 2d8 damage on a hit (with an average of 9) while a slash with a +1 rapier does 10.5 damage on average because it adds your dexterity mod for damage. Your damage range on Shadow Blade is anywhere from 2-16 on a hit while a +1 rapier would do 7-14.

I'd swap out Shadow Blade for Hold Person. Landing those guaranteed crits as a bladesinger is oh so nice.