I've had a look at the Britmodeller article and, whilst there is a lot of very good information, there are also a few misinterpretations.
One that I quickly noticed, though not relevant to this discussion, was the incorrect identification of the seat harness colour, where a shoulder strap is seen hanging over the cockpit sill. The strap in question is from the parachute harness, and not the seat harness, confirmed by the "buckle", which has the hole for the harness locking lug, whereas the seat harness ( a different colour) utilised the "lever lock" system.
Also, there is some misinterpretation of what is, and what is not, some form of cladding, or cushion, on the seat back, where some of the photos definitely show the seat without any form of cladding or padding. (note that some photos shown are not WW2).
However, in some of the photos, there is evidence of some form of cover and, in some instances, what appears to be a thinly padded cushion, not the bulkier flotation device type.
I've had a closer look at the photo Geo posted and, in my opinion, I think that the seat back has a canvas, or similar material, cover over it, close-fitting, and following the contours of the seat (note how it "curves" around the top), rather like those elasticated car seat covers from years ago.
Examples are clearly seen in some of the wartime photos in the article.
I can only think that this may have been fitted, to some aircraft at least, to prevent possible wear to the parachute pack, and / or the pack closure flap.
Although this would be similar to the covers seen in some of the Britmodeller photos, I may be wrong, and it might indeed be a thin cushion, as also seen in some of the photos (along with seats lacking cover or cushion).
I think that Geo's representation is acceptable enough, and is more accurate than portraying the thicker, yellow flotation device cushion, which I'm fairly sure would necessitate the use of a seat-type parachute pack and, as far as I'm aware, was not used in the ETO.
Jut an interesting snippet concerning an ETO P-51 ace (ashamed to admit I've forgotten his name !) who got hit over Europe and his Mustang exploded. He found himself in mid air, pulled the rip cord at relatively low level, and landed in the shallow water of a pond, in a sitting position.
When he tried to stand up, he discovered he was still strapped to his seat !
He was equipped with a back-pack parachute, and the pilot 'chute had managed to deploy, between his body and the seat back, successfully deploying the parachute canopy. If he'd been using a seat-type parachute pack, this would have been impossible, and he would not have survived.