It sounds like a cattery might be best with a cat so nervy, rather than them get stressed and go into hiding. It's what I'd do in your position.
A cattery will be £6-8 per day but probably give you a discount of a pound or 2 for two cats sharing.
Ring around a few in your area and go visit make sure you're happy with the facilities and the condition of the pens (e.g. do the litter trays look clean, will they be warm enough etc.). Bear in mind there will normally be drop off/pick up times say 10-12 and 4-6 so plan around that.