Buy a single air ticket to Kuala Lumpur on air Asia to give you a departure date of Thailand within 30 days of arrival. That will clear any potential issues boarding you UK / Thailand flight.
About a week before your 30 days stamp expire go to immigration to get a 30 days extension .
At the end of your 60 days in Thailand go to cambodia for a few days to see the temple and get stamped in again for 30 days coming to Thailand ( same applies, you ll might he asked for a return ticket with a date within 30 days of coming back to Thailand.
You can extend again by another 30 days.
If you don't have a passport showing loads of back and forth to Thailand you ll be fine .
Don't take the habit to do this or one day you ll he refused entry into Thailand