I booked the boys into a lovely cattery for their first holiday and they HATED it. Riley (the friendliest, happiest, most confident boy) hissed at the cattery lady and one of them wee'd in their bed
They have never had a non illness related accident or a non 'stupid Mummy closing the door to the room with the litter tray is' accident before so they must have been pretty unhappy to wee in their own bed
This was despite the cattery being positively luxurious and the lady a true cat lover. Ever since then I've gone down the pet sitter route, either a paid for one or my sister coming in twice a day.! The boys seem completely normal when I get back so pet sitter all the way for me.
I would be especially wary in your case that Ella will have to 'put up' with Archie in such a confined space. At least in their own home she will have many more hidey spots.
If you go down the pet sitter route you can meet them beforehand to make sure you feel comfortable with them. My boys hide when the petsitter is here but the rest of the time they are in their own home and their routine is pretty much as it is when I'm not there.
I vote.... Petsitter!
P.S If you do decide to go down the petsitter route, as your hols are in the 'peak' period you could ask the cattery that if they manage to re-book your space whether you could get a refund on the deposit?