To add to what Oliver said, all you might need bassinet-wise is your own blanket in case baby gets a bit cold.

The bassinets are clean and rather large, so at 4 months he/she will have lots of room too another plus is that it has a kind of belt, so if you strap the him/her in, you won't be required to pick him/her up if the seat belt sign comes on, unlike some other carriers.

We have always found LH to be a pleasure when traveling with a baby, e.g. the generous luggage allowance (lap children get 20kg), the nice bassinets, they will attempt to block the adjacent seat when travelling alone and the flight isn't full, the crews are generally very helpful, etc. I'm sure you will have a good flight.