Hi, Magdalen!! Welcome back to the world of stitching.
If you're looking for big projects that are based on fine art, I'm a big advocate of Scarlet Quince--
http://www.scarletquince.com/. I'm working on a world map from the mid 1500s that I found when I googled "Cross stitch world map," and I have since bought five more patterns from the company. The map will end up being 28 inches wide by 20 inches tall (71.12cm by 50.8cm), and they have even larger patterns there.
This is their Scream pattern:
http://www.scarletquince.com/pat.php?pat=MUN010" target="_blank" target="_blank" target="_blank
And this is their Starry Night pattern:
http://www.scarletquince.com/pat.php?pat=VGO003" target="_blank" target="_blank" target="_blank
There are other companies who provide fine art patterns, too, such as Heaven and Earth Designs, better known here as HAED, but I can't figure out their website to find just their fine art patterns since they did a redesign of the site. They also have very cool non-fine art patterns that are gorgeous in their own right!
Edited to add: Where are you located at in the world? In the United States, I would recommend getting supplies from a well-stocked online store like 123stitch or Everything Crossstitch. You can get floss bins there (I usually get mine at the local Joann Fabrics store in my town, since they always have some in stock), a craft bag to put everything in while you're working on it, and, my most recent discovery, Q-Snaps to hold your project in place.
I can't recommend Q-Snaps more to use in place of embroidery hoops or stretcher bars, especially if you're going to be working on a big project. They are PVC pipe in various sizes of squares/rectangles (I like the 11-inch square size, best for my rather large hands to hold) that you place the fabric over, and then use the plastic clamps provided to hold the fabric in place. The excess fabric that will be draped over the sides can be rolled up, then you add a Grime Guard around the square of pipe and fabric to protect the fabric from your hands (I didn't have this when I first started, and the excess fabric got a bit dirty from my skin oils, but I washed it) and, if you want, something to put between the fabric and the clamp (I use a six-inch wide length of white cotton that's long enough to go around all four sides, and after it goes between the clamp and fabric, I use the rest of the six inches to wrap around the excess fabric in the back and clip it all in place using a big hair clip that I bought at the beauty-supply store). There's a Q-Snaps thread in the Tips sub-forum that I posted some photos of my work in progress with the Q-Snaps holding it taut, so you can see what I'm describing here.
As for floss, look around at the various websites for where you can get some pretty cheap. The type that is most commonly used here in the States is the DMC brand, but I know that there are other types such as Anchor brand that other people here use. I have always used DMC myself, just because that is the most common one used in the patterns I have bought over the years. So, I have a big stash of floss bobbins in floss bins that I already had in my craft box when I started this map project. But, I did still have to buy a lot of floss to fill out my supplies for the project! My mom went to the store near her house (it's a regional company, not in my area of the country) when they had DMC skeins on sale, and she stocked me up with what I needed for a much lower cost than I would have paid online.
So when you get your supplies for a big project, keep an eye out for sales!
Something that I can recommend for all new or returning stitchers to look at are how-to videos on YouTube. I was really surprised to find that there are so many crafting videos to watch that can show you how to do just about everything you might imagine in every type of craft, including stitching! Definitely spend some time checking those out for tips, as well as asking here, of course!
Good luck.
Edited again to add--look around for a needle minder to keep track of your needles! These are magnets that you can put onto your project or Grime Guard to keep your needle in place while you're not working on the project. There are lots of really pretty ones available--I got mine through Amazon. There's a company called Puffin and Company that makes really adorable ones--I've had a bee and now an owl that keep track of my needles.
