Crazyone, this is a very interesting question that I've never seen before on the forum!
So first of all, I don't think you look "too formal" at all in your pictures. (Great outfit, by the way). But I don't share your problem at all, so maybe it'll help if I explain why.
1. I never tuck anything (mainly because it doesn't suit me; I have nothing against tucking in general, and it suits lots of other women). If the pants have big belt loops and need a belt, I semi-tuck the front and leave the rest out. This is automatically more casual.
2. I often wear a blazer, but always with a tee shirt underneath -- almost never a collared shirt. The odd time I do wear a collared shirt under a blazer, it's a fitted, untucked shirt (no visible belt) with the collar layered over the blazer collar, à la Saturday Night Fever. Again, less formal looking.
3. I have a moto jacket and a "jean jacket" that's actually made of black waxed cotton. Both get worn a lot indoors in the cooler months. They soft and flexible enough that I can wear it indoors without feeling uncomfortable.
4. I wear lots of loose, drapey tops with open necklines. They look more casual than blouses or shirts.
5. I sometimes wear a hooded shirt under a blazer, which is so incongruous that it looks cool (and definitely casual!).
6. I normally wear jeans, not office pants. Sometimes a skirt or a pair of leggings with tunic.