Cache plugin questions

Hi, I recently made a switch over to a new hosting service but my site has been suspended twice because the site has grown in popularity and somehow all these visits are spiking the db which in turn is getting my account suspended. I was told a cache plugin would help my case but with so many of them out there I don’t know which would be best so i’m looking for recommendations from the community.

Also how will the plugin help me in prevent me from spiking the server.