As someone who has exactly the same outlook, here are my top three tips for appearing quiet, but friendly:
Maintain a small repertoire of information about co-workers
One fact per person is OK, 2 or 3 for serious contacts. When someone asks you how you are, respond with something like "Fine thanks. I hope your sister is feeling better." Then nod through the (usually) short reply. It's especially effective in the case of family sickness, they will appreciate you remembered.
Use headphones to ignore what you want, be extra attentive when you don't.
Sitting in the middle of plenty of office gossip, you hear very little and can ignore the rest. When people do bother you, it will tend to be for a valid reason so before talking to them turn the music off/remove the headphones and turn and face them before speaking. If you give them your full attention when they need it, they won't mind when you don't.
Make a joke of it
For example, recently colleagues had a meeting in a room further away to normal.
When they came and explained they had been moved rooms (I hadn't even noticed they had gone) my response was "Sorry, I'll keep the noise down in future so you don't have to move away"
It lets them know that you know that they know. If it's clear you are comfortable enough with your quietness to make jokes about it, they won't feel uncomfortable on your behalf, or feel the need to involve you in things you may not want to be. Good co-workers don't want anyone to feel left out, but if it is clear you are happy left alone and won't feel aggrieved most will be equally happy to accommodate you without a problem.
In other words:
- Show you care a little
- Don't be unhelpful
- Make it clear you are happy being quiet
And you will have problems rarely if ever.