A couple of people have asked, so here's a rough guide to how I draft a sitting pattern. I didn't include details like pawpads, tail, ears, etc., this is just the basic stuff for the body shape.
Sketch of the side view.
Since the hing legs overlap the front legs, break apart the haunch into its own piece.
The belly gusset. Draw a line from the base of the neck to the front of the haunch (red). This gives you the basic shape of the belly. Straighten out the center (red) line. Add a dart in the 'armpit' of the foreleg, otherwise the front legs will splay out.
Duplicate & flip the drawing to get the full pattern piece. Add a short piece to widen the neck, if you need it.
Note the A (corner) and C (center line) of the read part of the gusset.
The A and C points marked on the body piece and the outer hind leg piece. Draw a curved line from C to B. This gives you the shape of the inner hind leg piece.
Add a dart to the outer hind leg to make it bulge out realistically. Draw a short line on the outer hind leg piece where the haunch is widest. This is where a triangular dart will go - because the dart will take away from the length of the seam, add a little extra material to account for that (the solid line outside the dotted line)
Drafting the center head gusset. Put marks around the outline of the head to break it into segment - marks should be at sharp corners and the center of long curves. Straighten out the outline as shown. Draw the outline of the gusset. This one has a narrow muzzle that widens at 3 where the muzzle meets the forehead. The forehead broadens to the highest point of the head at 4. Usually this part of the gusset is 2/3s the depth of the side head piece. It narrows down to a single point at the back of the head where it meets the neck, 5, but you could also continue this all the way down the neck and back for a fatter plush. Duplicate & flip the drawing just as you did for the belly gusset.
The width of the front of the gusset, marked in orange, should match the width of the neck part of the belly gusset. If you didn't add a neck, the center head gusset should narrow down to a point in the front as well as the back.