Why not get a one-year non-O by marriage from London Thai Embassy. No tickets or financials required , copy of marriage cert , wife's ID & blue book copied & countersigned . Its multi-entry & if used correctly could be extended up to 17 months.
Unless your ticket was bought from Samui to your destination as a direct thru ticket you will have to check in separately at BKK anyway for the Euro leg. New rules introduced by BangkokAir whereby Samui - Bangkok tickets purchased as a separate transaction , means you can no longer clear immigration or put through luggage to Europe at Samui airport
Depends on your budget more than anything as well as Visa requirements. Several companies do minibus including accommodation for 5 to 6k baht return or you can fly Samui to Phuket (BkkAir) to Penang (Airasia) for about 5k e/w.