I am sick of flights that are "preassembled" (I don't know the right word) by aggregators. I am willing to pay a bit more to buy one ticket and not need to recheck my bags at every stop. Further, I would like to be able to build in a fun day with a long layover in BKK. Are there any sites or services that let you choose all the legs and then buy it as a complete ticket?

I'm planning a multi-city flight over Australia-Thailand and Turkey. I have 6 months travel time. If possible, I would like to spend 4 or 5 months in Thailand. But I have a two month stay limit to Thailand and I can't buy tickets from Thailand for any time I want because I have to show a ticket to a non-Thai country when I enter Thailand showing that I will be leaving on time. If what I understand is correct, the reservation I am trying to make now shows a flight to Turkey two months later. It is not certain that I will be able to get a visa if I make my Thai exit date 4 or 5 months later. How would you recommend me to proceed in this case? If I make my ticket 4 months later, which is now two months later, should I enter and exit a nearby country? Thank you in advance for your patience and reading and replying to me.