Hey Tommy,
As I understand a bear minimum would be about 90x45cm, as it's recommended your tank be at least twice as long as at least as wide as an adult. If you're keeping a pair, you don't have to double that, but you should come close to double. (120x45 at least).
in fact I have never seen an adult Axolotl with a size of 45 cm - the largest that came to my eyes was 36 cm (and most I know kept in tanks get as big as 30 cm).
In my opinion you also do not necessarily have to have a larger tank for more than one animal, depending on the decoration.
I keep 4 adults (ranging from 25 to nearly 30 cm) in a 100 x 50 cm tank with many hides and a lot of plants (looks like a jungle sometimes) without any problems. As axolotls grow older they not only get larger but a lot calmer and less-moving, too.
I am partly with you concerning the water depth - Axolotls do not need deep water but some of mine prefer to hang out in some plants, sometimes near the surface and sometimes in the middle.
As you already said, water parameters are more stable the more water you have in the tank and therefore I personally fill my tanks up to 8 cm to the rim.
So in my opinion it is better to have a big tank but for a pair an 80 x 40 cm tank with many plants and some hidings.
But be aware, nicnic123: If you get infected with the Axolotlvirus you want to have more than one or two Axolotls (I have 28 right now...) and then you definitely need a larger tank, or a second one, followed by a third, maybe a fourth...