I buy whatever I can afford, from wherever I can get it. That has never been Amazon. My last cover I spotted when I was walking around the neighborhood. I RAN home, got the car, and successfully completed my first curb garbage dive.
They last a few years and then, the chlorine wins and the bubbles start coming off and they start to rip. So, get what you can afford, I have had all the different colors and I can't state one is better than another
About that 10 degree plan. What I have come to expect from the cover is that it will keep some stuff out of the pool until you take the cover off and dump it back in..lol. It will help to reduce temperature loss at night. It will heat the first 12 inches or so of the water during the day BUT the rest of the pool will be cold. Expect a few, 2-3, degrees of heat.
Your best bet is to get the cover and couple it with some solar panels. That's where you will see real temperature rise