Yes, they are difficult. Have you read the sticky on pairing?
All I can add is get the smallest juvinelle you can find. Introduce them slowly and be ready to remove it if the new one is getting beat up too badly. Make sure the new one has somewhere to hide if getting picked on. I saw a thread where someone used a water bottle, introduded the new tiny maroon in the water bottle. If the female picked on the little guy he could retreat back into the bottle and be safe. Wish I could find the thread, from several months ago.