Model 1943 tunic made of "herringbone" cotton twill or HBT, feldgrau colour. It is part of the suit (together with trousers and cap).
To choose the size use a flexible meter or at least a rope. Compare any jacket that suits you with the table below.
NA - neck around: the girth of the bare chest under the armpits.
SW - shoulders width (key size): from one sleeve to another along the shoulder seam and behind the neck.
SL - sleeve length (along the longest side).
First "Drillich" uniform was white and intended for work and exercises in barracks to preserve the "main" cloth form. Since February 1940 they started to produce HBT fabric in reed-green color for camouflage purpose.
The "Drillich" uniform was worn during marches and occasionally in combat. "Light" uniform showed itself practical and convenient, and at the beginning of 1942 the army decided to develop "summer" suits on the model 1942 suit base (pocket flaps were pointed). This form was worn with all insignia, as well as cloth one. Later model 1943 HBT suits appeared (simple rectangular pocket flaps).
Such suits along with caps encountered less often than the main (cloth) uniform. And cotton models 1944 never appeared, because the economy of the Reich was not up to "spare" suits by that time...