Hey Saswata. The HDD wouldn't affect the SSDs performance in any way. I guess that you are using your SSD as your main drive with the OS and programs on it? If this is the case, your OS and everything you load from the SSD will still be as fast as it is now, even after you install the HDD. Usually the SSD is kept for the OS and programs as I already said and people get HDDs for storage and games because of the larger capacity.
As for which HDD you should buy - it all depends on what you're going to use it for and what capacity you want the drive to have. If it's for general usage and you don't need more than 1TB capacity, then I'd recommend WD Blue. On the other hand if you are looking mainly for storage space provided by a drive which...