Hmmm ....

Your best would is a business class 'cash and miles' reward. At that time of year, the Middle East is a decent choice for some sun and Dubai is 30,000 miles in Business. Availability is a doddle, with IST-DXB, MUC-DXB, FRA-DXB and VIE-DXB in J available on that day - you simply need to find a decent connection from MAN. All these options also available on the 19th for the return. Swiss - whilst I haven't checked Swiss - is a good choice if you can get it because they now have fully flat seats in Business Class on the Dubai run (the others above - not sure about Turkish - are sloping flat.)

Cost - £75(?) for buying the extra 5k miles, £210 for the 'cash' part of cash and miles plus the taxes (£250?).

It would be cheaper doing an economy redemption, of course - 25,000 miles is enough to get you to San Francisco, for example, although 5 days is pretty short for a trip to the US West Coast especially in Economy since you need a day or so to recover. Your cash cost would then be £170 for the 'cash and miles' cash plus the taxes. The problem here is that you may find a cash ticket for not much more.

You might also want to think about the BMI mid-haul routes like Cairo, Tel Aviv or Moscow where you'll get a very comfy business class seat and where the weather will also be OK. Perhaps a bit chilly in Moscow, though!