What sort of things were you thinking of ordering online Shelley? I've been happy with the couple of tools I bought from Chillington Tools, and then there's Amazon or e-bay but do watch out for whether VAT has been added or not, and how much postage too which can make some purchases a bit more expensive. If you want seeds - then everyone has their favourites for reliability of seed, variety and costs and it could be a very long list. Johnsons seeds, Dobies, Suttons, Mr Fothergills, DT Brown, Thompson & Morgan, Kings Seeds, Moles Seeds, Premier Seeds Direct (on e-bay), The Organic Catalogue, Real Seeds are just some of the popular ones but there are many more - again, do check postage as some are free, some outrageous, and some only add postage for certain seeds like beans and peas or have a minimum spend.
Or you can call in somewhere like Wilkos in a few weeks time to pick up onion (overwintering type), shallot and garlic sets for planting, and from about January when the seed potatoes and spring planting bulbs are out followed by seeds - I've been happy with the ones I've got from there especially when growing vegetables for the first time, but when I wanted to try out different varieties, will often look at websites, including JBA seed potatoes (google for addresses) For plants online, my experience is very limited but I've been happy with the strawberries and rhubarb crowns from Mr Fothergills although I'm sure many of the others are just as fine but I do tend to look out for when they are on special offer (or the occassional free postage)
Be prepared to come across a whole new range of vegetables you don't find in the supermarket, and if unsure, you only have to ask what others thought about them before buying.
Good luck with the test in 3 weeks time - hopefully you'll be a bit more mobile and be able to visit some garden centres as well