I am very sorry you lost Thumper. Was he vaccinated? Getting a PM done will hopefully give you some answers.
All bunnies are different when it comes to grief. My boy, Fiver, was distraught after he lost his wife and I had to get him another friend quite soon after we lost her. Make sure your Pepper isn't showing signs of depression/loneliness. Usually if a bun is struggling over the loss of their partner they will decrease their eating, lose interest in their toys, become less active than usual, crave attention from other animals/humans, become destructive etc. These can be signs of an illness, too, so it's always best to have the vet check them out should you see any of these symptoms so you can rule out something medical.
Some buns seem to cope perfectly fine, especially if they've been able to see the body of their partner. This means they can accept what has happened and understand where they have gone and that they aren't coming back. In this case, I would wait until YOU are ready for a new bun before looking for another friend for Pepper.