10 gallons is kinda small. No worries though! Its all good. You can add a sump. How big can you go? I would suggest you add a 20 gallon sump if you have room. Gradually build up the total volume of water. Maybe take double your normal water change, add that water to the sump, and let it run without actually changing any water. (I'm guessing you do a 20% water change.) Next time remove one gallon while adding back 3 and so on until you have the total volume you want. Then do 20% water changes or 5 gallons.
Why do you think you need a sump? What are your long term plans? With a sump you can run bigger skimmers, add more LR (which you will need to do) and get better flow. What are you hoping to get out of the addition?