Hi,
You should be able to do that.
First, you could remove the third characteristic.
Then, in the variants tab of the product, you should have three types of variants:
- the variants when "just sole" is set to "please select" and "just strap" to something else
- the variants when "just sole" is set to something else and "just strap" to "please select"
- the variants when "just sole" is set to something else and "just strap" to something else
For the first type of variants, you can set the image of the sole, for the second type of variants, you can set the image of the strap, and for the third type of variants you can set the image for both the sole and the strap together.