I attach this (2019) "ETS Business Class Train" review for your info.
In case you may want to take this Business Class Train from K L Sentral,
Kuala Lumpur to Padang Besar (Thai/Malaysia border town). A Six Hours
trip. From Padang Besar you can take a Thai Shuttle Train to Hatyai
Shuttle train runs only twice a day. Please check it out.
Before the Covid Pandemic, there were six trips from KL Sentral to
Padang Besar. New trains include Business Class, Gold Class, Platinum Class.
The best is the Business Class. It was reported that the Malaysia/Thailand border
will open again from May. Please check it out. BTW, from Hatyai I would take
a Train to Bangkok after staying a night in Hatyai.
In closing I attach a (2019) ETS Business Class "video" for your viewing.
https://www.youtube.com/watch?v=p8ImH5H-18k