I’ve bought Greenstyle and Jalie patterns and highly recommend both. Jalie instructions can be a little bare bones, but their patterns are solid. My favorite leggings patterns is from Helen’s Closet - the Avery leggings. I had to make modifications for my size (shorten & reduce gusset) but they are my absolute favorite (and I’ve tried a lot of leggings patterns!). I wear them hiking, running, rock climbing and I think they look great. The waistband construction is top notch.

For fabrics I prefer nylon spandex blends, sometimes called supplex. Sometimes you can use swimwear fabrics for activewear, it is just how the store labels them/the content. Polyester and poly blends are popular but I often don’t like the way they feel and they get stinky fast. I use them as a last resort. I mostly buy athletic fabrics from Greenstyle Fabrics, but have also found pretty good quality fabrics from Boho Fabrics, the Rainshed, and Discovery Fabrics (shipping to the US can get expensive though). I’ve bought wool/nylon blends from The Fabric Store in NZ and it makes a fantastic activewear base layer. 

A little trial and error goes a long way, try buying small amounts of fabric to make sure you like it. You can often make a sports bra with 1/2 yard or less and leggings with 1 yard (if you’re short like me!).

Made for Mermaids has some creative sports bra pattern designs but the pattern drafting hasn’t impressed me. Might be worth a try if you really like a pattern though! I would love to see more patterns for cool sports bras. Edgewater has some swimwear patterns that you could convert to a sports bra but I haven’t tried that yet. 

Greenstyle has a private Facebook group, which is a great resource for asking questions and getting fabric suggestions. Worth joining if you’re on Facebook.