I think you will enjoy the Gazelle tent. A few people I know have recently bought them and love them and even I am looking for one for longer trips or for when I want more space.
At 51 with a history of BMX and skateboard related injuries and broken bones, yeah I get the whole "as you get older comfort becomes more important".
For the past few years I have been using a 1991 Volvo station wagon, rear seats are completely removed - it gives me a TON of space, is cheap on gas and has a good stock ground clearance - gets me 70 to 80 percent of where are real off road truck can get me. The thing has over 483,000 KM and my crew I do back country with all laugh every time I bring it along but we all love old Trinity.
I have been car-camping since I was a kid. Everything from full size GMC vans/converted cargo vans, down to a Jeep Liberty (that sucked for the record, slightly better than trying to sleep two adults in a 2010 Mazda 3).
The Volvo with high quality Thinsulate sleeping mats (self inflating) work really well. I have two 2 and a 1/2 inch ones, as well as two 4 inch ones. Both sets roll up tight and take up very little space compared to a blowup bed/Air bed. They are also WAY more durable. All four mats are now over twenty years old and still as good as the day I got them. The thick ones are Eureka brand and the other two North 49. People are always stunned how comfortable they are when the first use them. As others have mentioned it comes down to "Less is More" as well as using rooftop and back of car storage solutions. With the Volvo set up two full sized adult men (I'm five nine, my friends all seem to be over six feet) have enough rough to stretch out and have a good night sleep.
That all being said I also use/have an Eureka AT-4 all season tent. This thing is amazing in all weather, monsoon level west-coast rain storms that last for days and even blizzards and windstorms. Handles wind very well, and its design keeps heat in very nicely. But as I get older I am looking at the Gazelle and/or an off-road trailer solution.
I just purchased an 2002 GMC Jimmy 4 door which is going to be my next build for the back country and overlanding. Nothing extreme, no rock crawler, etc - just something with real 4x4, 2.5" lift, 31X10.50 tires and a bit more room than the Volvo. I have yet to measure it all out but it will be close to or hopefully slightly larger than the Volvo. I am not a fan of rooftop tents as I am okay with ground tents - so we will see over the next few years where things end up going as it were. Again with this build my big concerns is proper secure and water/dust-proof storage outside of the cab on the roof and out back of the truck (as needed). Figuring out what one really truly needs for a day, a weekend, a week takes practice and time - it's funny what things one will hold onto and what one can end up deciding one doesn't need. Quality and intelligent storage solutions (which typically means $$$) make a world of difference. I love my Pelican cases, ARB makes some damn nice stuff but boy it is not cheap. Things like recovery gear, medical/first aid and basic survival gear of course can't be excluded.
Health wise it is the cold mornings that kill me - and as someone who camps year round those morning aches in freezing or cold damn weather can suck.
To help with body aches and the cold I have learned everythign I can about aftermarket insulation (van has it done, Volvo is half done, Jimmy will get it done). While car camping a 12V car heater can provide enough heat to make a difference on a chilly night (ideally plugged into a house/second battery and not the primary/master battery). It really makes a difference.
As mentioned Fuel is an option.
I have access to a 1974 Dodge B200 raised roof van, upgraded to one ton suspension including a spring lift and all the steering goodies that go along with lifting an old domestic truck. Again it can go damn near everywhere (minus narrow & low hanging branches trails). But that big V8 318, raised roof and 18' length kills ones bank account when compared to say my Volvo or the Jimmy. But it does have a heater, stove, oven, fridge etc - it's a Class C old school conversion van.
Pop-tops.
I have seen them done to Rovers, Troopers (there's a cool build on here using one) and other mid-sized SUVs/trucks. Those who have them seem to love them - myself I have zero first hand experience. For myself, I have to ask about the loss of roof top storage can I load them up with stuff? They are not a cheap aftermarket solution but there are places that do build custom ones for clients around if one looks for them. With a good rear bumper storage system ($$$) and/or a rear basket I suppose one can use the back of the LC with ample storage room and sleeping space in the pop-top.
As stated... we all have our own opinions and ideas of what works for us. Keep us posted and let us know how you enjoy the Gazelle tent.