Ebrewsupply.com. ryan is more than helpful and his prices are cheap, plus he ships fast and has full kits with everything you need. If you are not into electronics, and dont understand the flow of things,.going with his kit is the way to go
As far as other recommendations... Idk, not sure what kind of probes the bcs uses, but remember, you often get what you pay for. I bought a ss float switch from China and when I installed it the nut rusted. I've since got two from Auber for a few bucks more but no rusting😃. I've also heard of people using cheap China ssr's and having them crap out.
Best of luck.
Maybe try a raspberry pi...