I've been in touch with Finn's family during the past few days and they have responded with some lovely personal messages. Lorraine, his mum, has nominated a local charity called 'Gold Geese' for donations in Finn's memory. At the moment they only take donations via bank transfer so I need to work out the logistics of including them in a fundraising raffle as I'd like to make it a lump sum transfer from TZers. A JustGiving crowdfunding page looks like a viable option.
Gold Geese uses donations towards spreading awareness, providing gifts and organising memorable events, as well as funding therapy and additional support for those children diagnosed with cancer and their families. Laura has received similar support from a small charity based in North Wales called Nicola's Fund so I'm well aware of how fantastic these local organisations are.
https://www.goldgeese.org/our-juice/