Antiviruses are an essential for keeping a computer to its optimum performance. So here are a few antivirus that are available for free and a useful.
Avast protects you against a bunch of security issues even with a free version.
Avg is an equally good solution for your need but Avg feels much more lite on your resources.
So Malwarebytes is not an antivirus its a malware scanner.
If your computer started feeling slow to you it might be due to malware accumulated on your PC.
So going for a malware scan can be a smart move.