If to ask before from people the best way to buy ledger nano, almost every expert will recommend people to buy it directly from ledger official site
I also recommend you buy from the official website.
Also you can think it over, Trezor and Ledger are basically as good. Maybe Trezor is also fine for you. (But I also have Ledger.)
Then there's a well-written post with the right guidelines, you should start by reading that:
https://bitcointalk.org/index.php?topic=5288201.0