I am so sorry for the loss. As someone else said acknowledging their parenthood is really important.
I also had all my flowers for the funeral done in silk flowers from the florist. They're really beautiful and good quality, but most of all I still have them all to keep as memories, and some decorate my house now that I'm a few years down the grief road. I always give silk flowers as condolences now. There is a certain irony of having to throw out deceased flowers a week after a funeral. Anything that you give them will become a special momento. You can also have a star in the sky named after their baby, I'm sure it could be found on google.

Big hugs all round during this tough time.