The specs on the 270s do state that a SATA SSD is compatible. I would not go any smaller than 240GB though. And if you want to move everything from the old drive to the new one, I would suggest using a program like Macrium Reflect Free available here. You can clone the old drive to the new one and the SSD will greatly improve performance even on a older system such as the 270s.
My Vostro 270s, which was purchased in 2013, takes some time to get started. I am thinking of installing a small SSD to improve the situation. I have been told to move all files in the current HDD to the SSD once I install it.  It seems that I can get a small SSD for $20 or less. What type of SSD shall I purchase? The current HDD, the D drive, used space is 166 GB, Shall I get 120 GB or 240GB SSD? Does PNY - CS900 240GB Internal SSD SATA ([URL] work?
What type of SSD shall I purchase?