Unfortunately SSD's don't really come with thermal sensors so when you install it the fans inside the Mac will run at max settings, it can get pretty loud. A good workaround is the use [http://www.hddfancontrol.com/|HDDFanControl]. This will allow you to control the fan speed.
Now for the SSD that I would suggest it has to be the [https://www.amazon.com/Samsung-512GB-2-5-Inch-Internal-MZ-7KE512BW/dp/B00LF10KTO/ref=sr_1_1?ie=UTF8&qid=1465402199&sr=8-1&keywords=samsung+evo+pro|Samsung Evo 850 Pro] but if you're looking for a cheaper option you could go for the [https://www.amazon.com/Samsung-2-5-Inch-Internal-MZ-75E500B-AM/dp/B00OBRE5UE/ref=sr_1_2?s=pc&ie=UTF8&qid=1465402373&sr=1-2&keywords=samsung+ssd|Samsung Evo 850] (non Pro) still has incredible read/write speeds. For mounting you can use this [https://www.amazon.com/NewerTech-AdaptaDrive-Drive-Converter-Bracket/dp/B005PZDVF6/ref=sr_1_2?s=pc&ie=UTF8&qid=1465402488&sr=1-2&keywords=ssd+bay+for+iMac|converter bracket].