It's a bit hypocritical of me to say this, since I do have an anemone myself, but I'd actually recommend not getting an anemone. A captive clown has absolutely no need for one. The reason I say this is that anemones still do rather poorly long term in captivity. I've read that the survival rate after 5 years is something like 10%. Since anemones can theoretically live forever, that tells me we have a long way to go before we truly know how to meet the needs of these creatures.
Switching gears, if you do decide to get one, just be sure to do your research first, and I'd suggest waiting until you've had at least a year's experience keeping corals. If I'd waited and gotten more experience with my husbandry techniques, I'm sure it would have saved me a lot of headaches with my anemone.