New car time, but no idea what I should be looking at

They don’t require any attention really

There's a huge difference between the Octavia and Superb. There is space in an Octavia, but it's not exactly huge inside, especially as far as rear seat space goes - probably similar to an S60 though. Biggest difference is from the drivers persepective - unless its a vRS, it's going to be a big come down from an S60.

A Superb is a much nicer place to sit than an Octavia, and the rear seat space is amazing. Definitely worth paying more for, in my opinion, if you are spending an hour or two driving around in it.

I'm no expert on autism but would a bright interior with lot of light entering be good for him. e.g. a car with cream seats and a sunroof vs the same car with grey seats and no sunroof. Also would la quiet interior be a priority.

OP, don’t buy a basic Toyota if you value comfort and noise insulation

People will tell you they are reliable etc but you will want to escape from that car after 20 min drive.

If you like Volvo maybe just stick with it and move up a few years for a fresh example if you can find one.

Not a big budget with current prices very hard to find anything decent and low mileage.

Possibly way wide of the mark here so I apologise in advance if I am suggesting something that would be a total non runner and please know it's a suggestion made in earnest.

If the motion and movement is a salve for your son, would something like a good VR headset & driving / motion type content help to reduce some of the time that is required to be in the car?

Most people say the Octavia has class leading rear space. The Superb is a different, higher class of car. Also class leading rear space.

That said many rear passengers will prefer the higher seating in a SUV.

OP, just a bit of an out there suggestion, but have you thought about a 360 degree projector to display on walls of room a projection of the outside world of a car in motion, or 3d glasses for your son to experience "motion" of the car moving, combined with speakers/earphones, to help him without resorting to leaving the home ?

While a bit out of topic, i am just curious if this is something you have looked into which might help with your son?

Its Cork. There are thousands of other cars for sale in Cork. From dealers, with warranty, and trade in facilities. Theres nothing inherently bad about a Fabia, but there are just much better options available. The car you linked doesn’t even have air conditioning.

Volvo to a fabia sounds like a step down. Don't mean in a snobbery way