Thanks CS, I have since done this, but this is what I was hoping to do:
When I had hotmail way back when, I was able to link a second hotmail account AND my uni email all to the one. So I was only ever logging into my main one and anything sent to the other two addresses automatically got forwarded there. Also, when I would compose a message, I would have a dropdown option at the top of which address I would be sending it from.
I can't seem to do any of this from gmail.