Keep in mind that temperature control on an aircraft is out of your control and varies from airline to airline. You may feel fine on some aircraft, too hot on others, and too cold on yet others.
As a result, I'd have a t-shirt at the ready to change into as well as a light sweater, if possible. I don't think your choice of pants will matter much although if you can squeeze it into your carryon, a light set of loose pants might be nice. I'm not crazy about sleeping in a shirt and slacks--for me, I don't do that normally and wouldn't expect to get a decent night's sleep if I did. Of course, changing in an aircraft's bathroom can be a cramped affair, but I think it puts you more in a "sleep mode."
Definitely take advantage of the showers when you arrive. That step alone generally helps me rejuvenate and stay awake longer so that I can make an easier adjustment to my new time zone.