Tips, suggestions on what type of solar cover to buy & where?

[MTU 5.0]

I have a 24' x 15' AG that sees full sun all day long and I am looking into getting a solar cover and would like suggestions on who makes a quality cover at a good price and what type is best. My two reasons for getting a cover are to increase the pool temp (duh) and maybe retain some chlorine. Not sure how much covers help with the latter, but it would be a nice added benefit.

Do I need 12 or 15 mil or is 8 good enough?

What pattern and color should I look for?

Any suggestions on websites with good deals on quality covers are also appreciated!

Thanks in advance!!