Welcome Paul!
I'd recommend a Rigel Quikfinder, available from
Telescopes & Astronomy as it's small and light... I use one on my 8SE. It makes alignment easier than the Celestron one (in my opinion) as it displays a couple of concentric rings 0.5 and 2.0 degrees in diameter rather than just a dot in the centre.
The Telrad is another popular red dot finder but is significantly larger and would practically run the length of the 6SE optical tube!