Another possibility:
Could you manage a Thursday-to-Sunday long weekend (because of restrictions on when there are flights)? If so, you could try Prague (which everyone seems to rave about). Based upon flying out at 0730 on Thurs 9th August (arriving 1045) and coming back at 1645 on Sunday (arriving at 1800) Jet2 will fly you there and back for a total (for two people) of £224.96.
or, for a Friday to Monday break, Jet2 will take you to Krakow (which, I'm told, is stunning) for £229.96. [Out at 1450, arriving 1825. Back at 1900, arriving 2035].