I have been looking in to it and I have found a travel company that would let me go to: Cambodia, Lao People's Democratic Republic, Malaysia, Singapore, Thailand, Viet Nam. It would starting in Hanoi, Viet Nam an end in Singapore, Singapore.
Accommodation: 41 nights hotels, hostels, guesthouses & homestays, 1 night on junk, 4 overnight trains, 1 overnight bus
Meals: Some breakfasts, meals on Halong Bay junk & hill tribe trek
Excursions: Grand Palace, Angkor Wat, Cu Chi tunnels, Cameron Highlands tour,Vang Vieng bicycle tour, Luang Prabang waterfalls, Opium Museum, hill tribe trek, elephant ride, bamboo raft ride
Transport: Local public buses, minibuses, trains, taxis, boats, on foot
Group: Average 8-12, max 18. Due to the modular system of our tours some passengers may join or leave the tour at different times
Age: Recommended 18 - 60, recommended max 70.
Staff: Tucan Travel tour leader, local guide.
All of this is going to coast me 3020 USD
I am really looking in to it.