Можно сказать "я без слов" как "I'm speechless"
Sounds strange tbh
Does "у меня слов нет" work just as well or does it change the meaning?
It works but it is less common and it is more often used as an introductory phrase (with emphasis on "слов"):
It works just as well. It doesn't change the meaning
I have been told that Нет слов is a typical phrase in Russian, meaning basically this.
Should it be accepted here and if not, why? :)