First trace a mirrored copy of your basic block so you have full back and full front.
On both pieces, drop armhole by 1,5 to 2cm.
Draw the new waist line:
- slanted on the back: 2cm below waistline on right side and 5cm below it on left one
- with a V shape in front matching the side position to the back. Draw the V apex approximately in line to bust point, 10 to 12cm below waistline.
Starting from V apex draw the left neckline and where it meets center front start drawing its right side.