Help modelling palm of a prosthetic hand

[Rhadamanthys76]

I hope someone can please help me with this because I'm at wits end

I've been trying to make a prosthetic hand (3d printable) starting from this SW model of a human hand (

https://grabcad.com/library/human-left-hand)

I managed to make the changes to the finger joints and they print and bend well. Its all good to the terminating joints at the palm

I cannot proceed however; Since this is a prosthetic (for people with missing fingers), the palm needs to be hollowed out and raised for the user's residual palm

My Solidworks skills are pretty basic and I've tried all the features I know and tried experimenting with ones I dont, but I cannot seem to get past this

What I need is to modify the palm - the front portion

needs to get raised slightly, extend back towards the wrist, needs to be hollowed out and have a cutout for the thumb

Basically it needs to look like this palm

I've gotten as far as cutting the front portion of the palm and creating the sketch at the sides of the wrist, but I simply cannot get that to terminate at the palm
The furthest I've gotten is making a surface, but then it wont thicken and cant convert it to a solid

I would greatly appreciate some help on this
Thanks