Similar to some of the other commenters, I’m a native English speaker and (especially now that I have an ereader) I’m often looking up words. Previously when reading physical books, I’d just go off the context and assume I vaguely knew what the word meant, because looking it up on my phone would be quite time-consuming. However now that I have the built-in dictionary on my ereader, I’m constantly using it. Does it slow me down a bit? Yes, but I think it’s worth it. I see words popping up regularly that I was unsure about before but now I can define.
Ostentatious is a great word for example!
You said you were worried about not remembering them - Is there any way you can save the words you’ve looked up? Kobo has a cool thing where you can add these to ‘My Words’ and you then have a list of all the words you’ve saved, with the definitions to look back on. If you’d like you can then go through them to revise and hopefully they’ll stick in your memory.
By the way, I would have assumed that English was your first language! You write extremely well.
BlastboomStrice