Can I let my baby to sleep in playpen at night instead of in baby cot? Which brand of baby playpen to recommend?

Yes. You can for infants. As for brand wise really depends on what you like. I. Personally like Graco and chicco. Their stuff are relatively good and value for money. They have a large variety as well. You can see if you want something with a changing area, night lamp or even toys. And select from there.