TUI bringing car seat on board

Hi 

We are flying package holiday with TUI to Lanzarote with 3 kids 8,6 & 2.

The 2 year old already has their own seat but I am looking for advice regarding getting an airlineapproved car seat for them to bring onboard the plane. TUI have confirmed this is allowed and the seat needs to be 40in and ECE R44 - 03 approved.

Does anyone have 1st hand experience on what seat meets this criteria. 

Thanks