There are many excellent filtering systems available and it may be best to test a few for a week or so before progressing to a full purchase.
It would also be prudent to get professional advice as this particular area of technology may be seen as contentious. Ultimately, many companies allow reasonable use of the internet for personal reasons just as they would for using the phone, but suffice to say that the internet, while a useful tool and email a great way of communicating, can be misused and prove to be distracting.