Hi Jeff,
Tumbleweed usually blows through threads for projector screens, but hopefully can point you in right direction.
For £200 pounds you are going to be a bit limited in terms of optimising screen to projector.
Factors to consider will be the amount of ambient light in the room and the distance of the projector from the screen.
The more light in the room and further from screen, the more gain (reflection) you'll potentially need.
Also, I don't think there's a vertical lens shift on the 1200, so need to consider how far the ceiling-mounted screen needs to come down to align with the projector - i.e. how much black border to you need at top?
(different screens have different sized margins - I had to get extra black so that the screen viewing area would be at the right level for my projector.