You do not need to worry too much about size — I myself have two rabbits, one of whom is x3 the size of the other and they are fine together. If anything, it’s helpful that the smaller is the more testy one, as his nips do not bother the larger one. That being said, it would be a different story if it’s the other way around.
If you feel you will continue to take the utmost care and attention to your rabbits, regardless if they have a bonded mate or not, and you feel Olaf would benefit from a friend, then I would encourage you to try and find a match. Again, at the time when Olaf unfortunately passes, the younger rabbit may or may not react significantly. and if it is significant and you are willing to put in the extra care, grieving rabbits survive and recover, just like grieving humans.
The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.