I agree with @tony54143fcdd2516652c9e275, with that much visits per day, it’s possible you’ll need to upgrade pretty soon however until then, I’ll recommend to create a droplet using bare CentOS 7 and install the needed packages to run your Wordpress site on it.
Another option would be Ubuntu, however I feel like CentOS is perfect just for such situations.
Differences between CentOS and Ubuntu
The biggest difference between the two Linux distributions is that Ubuntu is based on the Debian architecture while CentOS is forked from Red Hat Enterprise Linux.
CentOS is considered to be a more stable distribution compared to Ubuntu. Mainly because package updates are less frequent. This can also prove to be a disadvantage of CentOS. If you want the latest version of a certain application or software, you will have to install them manually.
Ubuntu certainly has the upper hand when it comes to tutorials, online communities, and books. Finding solutions to Ubuntu problems are a lot easier than in CentOS due to its fairly smaller community and lesser available documentation.
Let’s wrap this up
If you are a beginner: Go with Ubuntu because it has a larger community, a larger reservoir of free tutorials and a lot more frequent updates to help you stay up to date.
If you are a business owner: CentOS is the ideal choice between the two if you run a business because it’s (arguably) securer and more stable than Ubuntu, owing to the lesser frequency of its updates. Ubuntu has its pros as well but there can be scenarios where you have to revert to older versions because of a new buggy update. Additionally, CentOS also comes with support for cPanel, which is something that Ubuntu lacks