The first step is probably a realistic analysis of your needs and budget.
On the needs side:
- Do you need a color printer, or is black-and-white enough?
- Are you just looking for a printer that will allow you to make more copies per month, or do you want one that will add more functionality than your current printer (e.g. double sided, additional paper sizes)?
- How many pages a month do you realistically need to print (on average)? If you expect the office to continue to expand, make sure you figure in growth in the number of monthly copies.
On the budget end, make sure you know how much you can spend on the purchase of the machine, a maintenance contract (if needed), and the ongoing cost of supplies (toner, etc.)
This isn't intended to be a complete list, but it will get you started. With this additional information you'll be able to research what's available and fits your needs. If you post more details here, some of us will probably be able to give you recommendations.