Are you sure you actually need a static IP address? There's obviously nothing wrong with having one, but if your just going to be editing your hosted website you won't really need one.
You can go for the subscription services such as BT's ones, and for starting up alot of people find it very usefull. However others prefer to a package which they setup on some hosting, as you usually have more control over changes & design.
On the subscription side have a look at openmindcommerce
- I've never used it personally but know many on this forum who have.
Another option are opensource packages such as OsCommerce, Prestashop etc. These are free and you would just have to host it. However you would probably need to spend a bit of money customising it to your needs.
If you going to be selling clothing will you need many "specialised" components (customisation, size / color attributes etc)?
I hope this helps,