I tend to stick to high street shops that have online shops as I am familiar with the sizing and can take the back to the shop.
However my favourite thing about online shopping is cash back. This is where you do your normal shop but go through a cash back website first in order for them to request a percentage of the purchase value from the retailer to be paid back to you. I don't know how it works but it does and I have rant about £10 back over the past couple of years.
It can take a couple a weeks or a couple of months but it's better than nothing.
My favourite websites are;
Also you get free money if you successfully refer other people to sign up.
P.s I have yet to try online supermarket shopping for food but it sounds convenient so I will up date you if I do