As mrmoo says, there are new covers designed especially for the Glo, but they don't seem to be available yet, at least not in the UK.
The salesperson in WH Smith is wrong, so they should just give you a refund. Though what you do in the meantime while waiting for the cases to be available here, I'm not sure.
There's not a huge difference between the two, but the Glo is a bit shorter, which is why the Touch cover isn't really suitable:
Glo: 114 x 157 x 10 mm
Touch: 114 X 165 x 10 mm