Hello and welcome

Great to hear that you've got back into fish keeping, and that your other half is joining in.

Large pieces of wood - try Gumtree and ebay.
If you can't find anything you like there, contact Aquarium Gardens and ask them the size of their largest pieces. I'm not 100% sure about bogwood, but I saw some huge pieces of driftwood there last week. They may also be able to get hold of what you want from their suppliers.
I hope that you plan to provide us with lots of pics of your tank as you are setting it up, we love pics.
