Most Canadians take the western route via Japan, Taiwan or Hong Kong. But don’t forget routes via Europe or the Gulf States. In particular, Turkish Airlines offers a reasonably-priced business class with wonderful food and a free hotel stay on a layover in Istanbul which would break up a gruelling long flight into manageable pieces. Many consider Emirates as one of the world’s best carriers. THAI from Munich and Istanbul has spiffy new A350s and has regained its mojo especially in business class.

As for domestic flights within Thailand, there are several highly competitive low cost carriers which offer reliable and inexpensive service all over Thailand. Notably, Air Asia is considered one of the world’s best airlines. These need not be booked very far in advance.

--Looking for any advice regarding what airlines to fly and what fare/class to choose--

That's entirely up to you. Most people just go with whatever airfare is cheapest (even more so these days). Some choose airlines because of loyalty schemes or points. It's a personal decision.

--I've been told it's best to arrange flights within Thailand after we've booked the international flight--

Yes you can arrange your domestic flights independently

Use a search engine to do some research of what flights there are, total travel time, transit stops, price and arrival/ departure times.then make a decision on which airline . But book directly with selected airline

Class of travel only you can decide if premium or business is worth it for you

**do some research of what flights there are, total travel time, transit stops, price and arrival/ departure times.**

^

+1 to that!

When I first started visiting, I would take an appr 10am flight from JFK/EWR...which got me to Bangkok the next day at appr 5-6pm.

I now prefer to take an appr 1am flight which gets me into Bangkok at around 10am the next day. Both had an appr 2.5 hour stop at HKG.

Back like 6 or 7 years ago when I was looking for business class bargains, I saw a deal on Austrian beginning in Toronto, connect Vienna, then BKK. I grabbed it and later got the positioning flights to work. The point is that I'm always looking. I search the heck out of a route and various deal blogs and Flyertalk, then pull the trigger and don't look back. Good Luck.

Some very good tips above.

To add to @Alistair N comments, please also play around with the dates. Moving flights by a few days can change the prices.

Given the distance, there are no direct flights. That leaves you also with various options to may break the trip and visit a place on the way there.

"I've been told it's best to arrange flights within Thailand after we've booked the international flight." Yes, you can do that. But on in- and outbound flights, having flights on one ticket is beneficial, as you have a guaranteed connection. For sure I would not risk a very long and expensive long-haul ticket on the inbound to save a bit on a domestic ticket.

Google flights is always a good place to start:

https://www.google.com/travel/flights/search?tfs=CBwQAhoeEgoyMDI1LTExLTEwagcIARIDWVlacgcIARIDQktLGh4SCjIwMjUtMTEtMjRqBwgBEgNCS0tyBwgBEgNZWVpAAUgBcAGCAQsI____________AZgBAQ&tfu=EgYIAhAAGAA&hl=en&gl=ae&curr=AED