Yes you are correct that the pilots had many problems with keeping their boots on when parachuting from their planes almost everyone did. There where many models of boots created during the war - some just to try to cure this very problem. The most common boot available to pilots in the summer 1940 was the pre war 1936 Pattern boots like the basic un-textured model above (it's very accurate).

The boots that followed this model where the following:

Pattern 1939 (P-36 boot with just a canvas top desert use only)

Pattern 1940 (leather uppers, gum rubber soles and a zipper in front (no straps))

Pattern 1941 (P-41 boot with big strap added around the ankle to keep them on better)

Pattern 1943 Escape Boots (zipper on side of uppers, lower shoes looked like a plain civilian - the tops were cut away with a knife after they bailed out in enemy territory, so the would blend in better)