I have spent a lot of time in that part of the world.
I cannot imagine wearing tights there so like your second outfit much better, but I would recommend ditching the boots. I think you will just be hot and uncomfortable - it is WAY too humid there for over-the-knee boots. Try finding some sandals instead - I think you will be a lot happier, plus you won't need to worry about packing big boots!
Have a great trip!
ETA: Remember that April/May is the hottest time of the year there, so the temperature is actually ramping up right now. You aren't likely to see anywhere near 22C outdoors in KL. But you will definitely need a cardigan or jacket indoors because I find the A/C can be cranked up quite high.
More editing: Sorry, I'm going to edit this again. You haven't specified whether you are going to be in KL or elsewhere. If you are in KL, you will probably be fine with a shorter dress (though I personally wouldn't wear such a short dress there - but that is just me). But if you are anywhere other than KL, the area will likely be much more conservative and you might want to consider a skirt that reaches your knees, or a pair of linen pants. Just a thought. Now I will stop!