From what I've seen, you're doing everything right. 2 out of 11 does seem like a lot, but some years are like that.

I've had chickens for 14 years, and up until last year only lost one chick (that TSC threw in because it wasn't doing well). Then last year I lost several and this year I lost one.
Heat plates are the way to go. I know everyone has their opinions on that, but I lost a lot of chicks last year due to my heat lamp. I used to use a heat lamp up until last year, but we had a really hard time with controlling the temp for some reason. Now that I've switched to a heat plate, I will never go back. My chicks seem healthier, happier, and feather out fast using the plate.