Hi Breakin Newz,
Yes … I would definitely get a mattress protector. Sheets don’t do a good job of protecting your mattress from body oils, perspiration, or accidents and stains to protect your mattress from damage and maintain good hygiene and cleanliness. Any stain (even a watermark) can also void your warranty.
There are different types of mattress protectors though (see post #89 here) and your choice would depend on which of the tradeoffs are most important to you.
Phoenix