Marley, like the wise man who runs my gym says, "Once you go Lulu, you never go back." I am seriously addicted at this stage, but I think you can do all sorts of tricks with non-Lulu. It's all about the sports bra, top/top, and leggings, with layers over. I have a number of simple tunics and long cardigans (James Perse, CP Shades, Madewell, Steven Alan, Inhabit, Rag and Bone, Enza Costa, American Vintage, Velvet, Eileen Fisher, etc etc) that layer easily so when I get to the gym, presto chango. Swap shoes, pull off the tunic and cardy, and go. If I don't mind swapping pants then I get even more options. This formula is also handy for dressing afterward, and makes less laundry.
I will go on record that all the moms who come to school dropoff in their skintight Lulus may look very fit, but cmon girlfriend, it's the easiest thing in the world to throw a tunic or cardy over AND JOIN THE WORLD. I only do it if I am coming immediately from training, and since I am sweaty and smelly, I like to think it's a different kind of inappropriate.