You will need an A4 Visual Arts Diary for your Lapbook. I recommend you purchase the Visual Journal from School Club* because it is Premium Paper, double spiral bound, has a plastic cover, elastic to keep it closed, has a pocket in the back and is oversized A4 - which means you don’t need to trim A4 Paper to glue in.
The School club also has A5 Hard Cover Journals for Nature Journalling.
You can use the same Journal for all subjects together.
You can use the same Journal for multiple children if you prefer
*School Club offers Simply Homeschool Members a discount - to receive this please register and sign up as Teacher and refer Simply Homeschool as the company.