Most rabbits do love to be with their own kind, to snuggle, to groom, and just for the companionship, but there are also lone rabbits who seem perfectly content. You didn’t mention if Sylvia is spayed or not. The first step in bonding rabbits is for both/all to be spayed or neutered, then to have recuperated from the surgery. It’s generally easier to bond a spayed female with a neutered male, but you can bond rabbits of the same gender. If you adopt a rabbit from a rescue, he should already be neutered. Some shelters will also spay and neuter their rabbits before adoption. That saves you time and money. Size doesn’t matter too much, but since Sylvia is a Flemish Giant, it might be better to get her a companion that isn’t one of the smaller breeds.
Here is an article regarding whether one should get a second rabbit: http://rabbit.org/faq-should-i-get-a-second-rabbit/. I really love seeing rabbits have another rabbit companion, and I have had several bonded pairs over the years.
Here is one good article on bonding: http://rabbit.org/faq-bonding-multiple-rabbits/. Sometimes bonding can be quick and easy, but in other instances, it can be difficult, frustrating and time consuming.