I think you are right. I looked into this last year. You need a different visa to go over that way. I changed my plans because of the long bus journey. You can do it in the other direction, Vietnam to Laos. Here are the ports for evisa.

Important Notice: The entry port must be exact and cannot be changed once the visa application is submitted to the Immigration Department
Can Tho international airport-Can Tho
Song Tien land port- An Giang
Cha Lo land port- Quang Binh

Da Nang international airport-Da Nang
Tinh Bien land port –An Giang
Bo Y land port- Kon Tum

Noi Bai international airport- Hanoi
Xa Mat land port-Tay Ninh
Lao Cai landport- Lao Cai

Phu Bai international airport-Hue
Mong Cai land port-Quang Ninh
Ho Chi Minh Seaport-HCM City

Phu Quoc international airport-Phu Quoc
Moc Bai landport-Tay Ninh

Cat Bi international airport-Hai Phong
Lao Bao land port-Quang Tri
Nha Trang seaport- Nha Trang

Tan Son Nhat international airport-HCM city
Ha Tien land port-Kien Giang
Hai Phong seaport- Hai Phong

Cam Ranh international airport-Nha Trang
Huu Nghi land port-Lang Son
Hon Gai seaport- Quang Ninh

Nam Can land port-Nghe An
Cau Treo land port- Ha Tinh Da Nang seaport-Da Nang

There's a daily Phetprasert bus that starts in Chiang Mai, stops in Loei, Udon Thani, Sakon Nakhon & ends at Nakhon Phanom. I took it as far as Loei once and was nice bus - look for pic of their schedule about half way down this web page - http://hobomaps.com/TravelChiangMai.html

Islands of Ko Chang and Ko Kood (Kut) in eastern Thailand have had problems with malaria in the past (including deaths) not sure what current situation is . There is malaria in Mae Hong Song province although declining.

I think I'll stop in surathani on the way back then, there's a direct bus/van from penang
So it would be sonething like this

Bangkok-Chiang Mai (pai and back)-Kuala Lumpur - Borneo - Melaka - Cameron - Penang (Langkawi and back) - Surathani - Bangkok

I think I'll stop in surathani on the way back then, there's a direct bus/van from penang
So it would be sonething like this

Bangkok-Chiang Mai (pai and back)-Kuala Lumpur - Borneo - Melaka - Cameron - Penang (Langkawi and back) - Shrathani - Bangkok

Hello I will be in Thailand the very
beginning of 2020--four days Chiang Mai, 3 Bangkok, four Khao Lak- and will want to buy some custom or customized women's clothing (and perhaps a suit or shirts for my husband). Has anyone recently done such there and can you tell me, does it need be Bangkok only, and is the timeframe unrealistic? Is it safe to measure/pay and then receive clothing later by mail? I have done some reading and am aware of constraints but am looking for any/all input.

Great appreciate!

2.5 weeks is not a lot,but you can fit in a 3 stop trip......Bangkok,Siem Reap and a Thai island...flying between them.If you really want to squeeze down your time in each,you could even fit in Chiang Mai (personally I wouldn't,but its possible).There are plenty of cheap flights.

Its a good idea not to try and fit in Laos and Vietnam too..you really haven't got the time ;-)

My only real comment is that i would either get straight Chiang Mai that evening or just have one night in Bangkok at the start and have all the Bangkok time at the end. The first we did had just a quick night in Bangkok at the end but felt we lost some time that way, so had the majority of our Bangkok time at the end of the holiday.

You could even get the train on your arrival night, take the cab from BKK to Don Muang, and get the later sleeper not much point in arriving in Chiang Mai at 7am.