Stretching the vamp is time consuming & difficult. I have had success in the past with full bodied shoe trees. I use a pair that compression fit the shoes I am working on, ie no spring.
I prefer shoe trees where the widest , fore-foot if you will, is split in two & allows me to use a form or spacer to adjust & achieve the width I need. I will keep increasing this width as allowed, while simultaneously laying dense cardboard flat on the insole to increase volume vertically.
If there is a removable insole in this shoe, take it out. As I am sure you have noticed with wear a foot conforms into the sole & thus increases volume over time. As this process happens the insole can later be added back into the equation.
I will also drill into appropriate solid body shoe trees to attach bunion stretchers in both the vamp & toe areas as needed.
No harm in using a shoe stretch solution as you go thru this process. I apply it internally with a sponge.