Just to add to this great advice, absolutely go with the white ( flat ) followers. If you can find reasonably priced mags with yellow followers grab them and replace the followers.You can either try to find one on ebay at a reasonable price (not), place a WTB post here... or roll your own by assembling one from parts.
I went with option 3... assembling from parts, which was also the less expensive option with the premiums being place by sellers on used mags.
Numrich (gunpartscorp.com) has everything except for the mag spring, but that's ok because Wolff Springs has them, and I would go with their springs in the first place. They also have used mags listed as being available... but that's an unknown, I would want to replace the spring, and maybe the follower if it's an older style yellow one and worn. The individual parts are new... so weight the pros and cons.