Tish I don't know much about adoption yet - as still only at the start of our journey - but just wanted to say congratulations.
I also wanted to answer your question about what to do to fill the time with a little one.
I have birth DD who loves craft and we do a lot of craft. We use every day stuff like safe junk, (cereal boxes, washed platsic food cartons etc, chocolate boxes etc), our DD creates robots, rockets and everything imaginable. We also buy paper, stickers etc to add to the materials we can use. We trail jumble sales and charity shops, and Christmas Bizarres, for second hand craft stuff. We also found the dressing up box a great play thing for DD when little friends visited (as I am sure they they will in the future). NCT sales of second hand toys are good places to get 'new' stuff and dressing up constumes.
You can also make stuff like bird feeders out of apples and yoghurt pots, and insect houses out of boxes and cardboard bits. Part of the fun being to watch for the visitors (not yet been brave enough to put the insect house in the garden yet!).
In the past few years we have tried gardening and we have enjoyed going out to all kinds of places like garden centres (they sometimes have pets!) and actviely look for places unusual to visit like the wolf sanctuary, which is only open about three times a year (yes, that will all be for the future when you are going out more).
I am hoping (if we are lucky enough to get through this journey) to collect the art work and other stuff the little one will produce. I'd recommend making compiling them into some sorts of scrap books all part of the fun, otherwise you end up (as we have) with a wardrobe full of art and no idea of when it was created.
IF your little one is not arty you could find a lot of other stuff, like music, listening to it together, making it together, making instruments (maracas) and recording the sound of playing or singing etc, making up songs together, or whatever.
If they are sporty have a sports day, running races together round the garden (if you are lucky enough to have the space) and playing simple versions of all the usual sporty things.
We have just found some of this stuff more fun, cheaper and more enjoyable than bought toys. You'll also find some things more enjoyable, if you record your fun with lots of photos etc it might help him later to identify what was good, what he's like to do more or again, especially if he doesn't always have the language to remember what you did, what you made etc. Does that make sense?
Enjoy it all and congrats again.