Ladies !! I need your help ! Sexy lingerie advice!!

Okay so for a long time I've been wanting to buy myself a cute/sexy lingerie or outfit ! But every time I order something online or go somewhere I get so scared to buy it , like what if it don't fit me . And also I dont know where to get good ones ! I always see some at Spencer's and stuff but that's way too expensive and I'm super shy to buy it in the mall !

Any of you ladies know of a good spot to buy lingerie?

Online ? Maybe in stores ? I've been to mega castle store and fascinations! (Arizona)

But I can't find any in my size .

I'm originally an xl/xxl in underwear ?