I would use the free version of Avast as an anti virus. No need to disable Defender as it will be done automatically. download site. Scroll down to select the free version download link. Remember to untick the offered Google toolbar etc. when downloading. You will need to register with your email.
For antimalware try the free version of Malwarebytes antimalware, the free download link is on the right, click here.
Later on you could search for a one-off payment licence for it for the premium version.
As a blocker I would suggest the free version of Spywareblaster. click here , the free version you will need to update manually once in a while.