Thanks for all information and advices, but I will go probably in middle june. It's rainy season but fuck it 

I'm probably going to try to make it over to LOS in the low season myself.  I don't mind rain terribly and I think that less crowds to deal with would be nice.  Just as long as the ladies aren't staying home.

The nail on the head @Unavowed. I've seen my fair share of Accor hotels (Mercure, Ibis, MGallery, Pullman, Novotel, Sofitel) and never ever had to make this amount as a deposit. I don't see ot mentioned on their website either. Anyhow, it got reduced to 5k THB (which is like 135 Euro), rather easy, so not a big issue 

Thanks for the review@Denbosch1971

Asking for a 1k deposit per day is ridiculous. You mentioned that you used loyalty points so assume you use Accor hotels regularly in which case I can only guess the deposit request is due to the location and perhaps some ‘difficult’ guests!

I’ve stayed at the Novotel in Soi 22 (or was it 24) and find this brand to be a solid choice.

Update for Novotel in Sukhumvit Soi 4 I booked a standard deluxe room, with king-size beds arrived around noon, while check in time is 2pm, but the had my room ready by 1.15pm. They normally charge 1k THB deposit per night. But, 19k sounded little high to me,  so we agreed on 5k  The non-smoking room is meeting all my requirements. Great bed, comfy sofa, a small fridge and a small desk. The bathroom is spacious enough, with a decent shower (even for two ) and there's a daily supply of water, coffee and tea. The bedsheets are changed upon request and my room (21st floor) is made up around 10 am.  I didn't book breakfast (495 THB/day), since I prefer not to be bound to certain hours and there are plenty alternatives available within 5 min walking. There's a rooftop bar with swimming pool (shared wit Ibis Styles), but didn’t visit yet. Same for the gym, no clue whether there is one to be honest  Only small disadvantage is the 3 elevators. They are freakin' slow and quite busy. During my stay, one was out of order, which made it even worse. But since I'm not on any time schedule here, didn’t bother me much. Besides that, for smokers among us, there's one place where smoking is allowed, a wooden bench outside, facing the Kicking Donkey. Far from comfortable and between noon and 5pm in the full sunshine ... hot, hot, hot. Novotel is absolutely guest friendly. None of my ladyboy guests had to ID herself or was even stopped at the entrance. No additional charge either, for both ST and LT.  I booked my stay mainly with loyalty point, but at the reception I see the current tariffs displayed: 4150++ (a few days ago 4800++) for Novotel and 3200++ for Ibis Styles.