That looks like an AT bus card. I think I might have some XT SCSI cards in the loft, but posting to the US might be expensive. Let me know if you are interested.
So if I wanted a 3.5 floppy drive, it has to be DD and 720k? would I also need to buy another floppy controller or could I only have 1 floppy drive installed?
Correct - for the XT controller, you can't use a high density drive. That is, of course, assuming you have the stock controller. There were many hundreds of different XT clones and clone controllers out there. I'm assuming you have a genuine IBM XT with the original IBM controller.
And yes, you can have two floppy drives - they chain on the same cable. Any PC floppy controller will be able to handle two drives. You'll notice the floppy ribbon cable has a small section of wires twisted - the connector after the twist goes to the "A" drive, and the connector before the twist goes to the "B" drive. All PC floppies are jumpered DS1.