Changing the Monarchy

Anyone who knows us, knows that our two cats are like our babies and that they have been spoilt rotten.

By spoilt rotten I mean that they literally run the show at our house - and they know it. They often get given the best spots (sun, blanket, etc) in the house "just because", sometimes I don't even shout at them for making an "oopsie" somewhere because it's easier to just clean it up - which is very wrong, I know, (this however doesn't include the time they caught a bird, and that's a whole other story).
Our decision on where we want to move or when to go on holiday pretty much revolves around them.

For five years, we've been living in townhouses that have enclosed gardens. Great for us = braais, etc, and great for them because they are two cats who don't venture outside much (seek out other cats, jump over walls, etc). Problem. Now we've made the decision to rent something smaller from the end of the year to try and save a bit of money.  We're looking at smaller townhouses, and if it comes to that - moving back into a flat (preferably ground floor). So far, we're coming up with a lot of "no pets allowed" places (although, a friend of ours has said that it's usually not related to cats but more likely to dogs).

My problem with moving back into a flat is this. Our cats have been spoilt with living in a townhouse for the last 5 years, really having the property to themselves. A few times over the years the younger one has ventured next door to check out the company, etc but has always returned. The older one has had her days of venturing and luckily just prefers to be at home.

If we were to move into a block of flats that has a long garden that isn't enclosed, what are these cats going to do? Will they know where to come back to? They are both spayed, so I'm not worried about that - but they've been so protected, they're not the type of cats to get into fights and I'm a bit worried.

Am I being over-protective? Any advise from cat owners at this point will be very welcome and much appreciated!