Avionaut Pixel will tick all of your boxes :)
It has a great position for little ones, doesn't "lie flat" in the sense of reclining, but really that's a bit of a compromise anyway as any kind of movement in the seat is likely to affect the structural integrity. Instead it has a very nice supportive insert that holds the child in a straight line rather than a C shaped curve.
It's made from EPS foam which is strong so no worries about it being structurally unsound.
People on the car seat pages are also waxing lyrical about the new Britax Baby-safe Core, which is Britax's new basic offering.
Both of these fit onto the same adapters like Maxi Cosi, Nuna, Cybex etc.
I do think a lot of the features sold with the high end seats are just marketing and not particularly useful.
Ordinary baby car seats are already quite reclined, so it's perfectly fine to let babies sleep in them if they are already asleep when go to take them out of the car. As long as it's not used as a replacement for their cot, and you aren't keeping them in the seat all day going from house to car to pushchair back to car to house all in the seat, it's fine. Keeping them in the car seat all day is a problem, because the position is quite restrictive for them whereas for their development they need the freedom to move around and roll etc on a flat surface. When travel systems were first invented in the early 2000s they were presented as this wonder solution which would do it all - car safety, often the ONLY option for babies <6 months on the buggy, rocking seat in the house for sleeping or playing, feeding chair (of course people no longer give runny purees to 3 month old babies so you don't wean them in a reclined seat any more!) and this was where you saw the problem of people overusing the seats, so started to see general warnings/advice about not overusing the baby seat. Now it seems to have almost overcorrected where people think they aren't supposed to let babies sleep in the car seat at all, which isn't quite right.
The general rule of thumb given is no longer than 2 hours in the seat at once. Which means if you do put them in the car, then put the seat on the buggy or shopping trolley then go back to the car, you're generally OK and/or would need to take them out for a cuddle.
When they are newborn (up to about 4 weeks) you should be more cautious and aim not to exceed car seat durations of 30 minutes. This isn't negated by any of the lie flat seats unless you get a carrycot style which is properly lie flat (but these take up 2x seats in your car and are outgrown sooner than the other types).