That one does look way too big for you! I've read that some people with smaller faces find the 3M VFlex works well for them, since it is a different design.
Personally, I've switched to an elastomeric P100 respirator (the rubbery kind with two filters and no exhalation valve) and find the seal is far better than I could ever get with a disposable mask. I use the GVS SPR644, but the SPR643 is the small size. Not sure if those are available in the UK, but there are a few options (Flo Mask, 3M, Dentec, etc).