How to choose an ecommerce theme?

Hello,

I originally built my website in Moonfruit, which is flash based and therefore far from ideal, but I know NOTHING about code and it seemed like the option to go for, as it’s really easy – you just move things about on the editing screen and upload graphics and pictures until it looks how you want it to.

Now, I’d like to start over, and WordPress has lots of lovely things written about it.

BUT, I really don’t understand how themes work. To what extent are they customisable? I need an ecommerce theme (doesn’t have to be free) that I can customise to build a website that looks exactly the same as my existing one (www.laurengrace.co.uk – but it only works on a pc – not mobile or tablet) but I can’t seem to find a theme that looks the same. If I picked a frame such as one of these: https://splashingpixels.com/ could I change all the page layouts to make it look like my existing site for example?

Sorry for the long post, I’m just really struggling with how WordPress works.

Any book recommendations that would help me understand also greatly appreciated.