Okay, you said you don't want to clip his frenulum just for the sake of breastfeeding but you must not be aware that a tongue tie affects everything including how a baby is able to move his mouth to learn to talk, to eat, and to even bottle feed.
My baby is 11 months old and although she is NOT tongue tied, she did have a tight frenulum. A certified lactation consultant, one who has the letters (IBCLC) after her name should have been able to adequately tell you that something is wrong. My lactation consultant worked with me and she did check for a tongue tie on my baby. She did not see anything obvious. When I went back to her for another follow up with her and it was obvious that my baby was still not taking an adequate amount of milk from me, she put me in touch with a speech therapist. I consulted with a speech therapist who was able to tell me that my baby's tongue was indeed tight but not in need of clipping. She further told me that with age, my baby's tongue would stretch and she even showed me some exercises to help strengthen her back and neck which would help my baby's tongue "stretch." What she had me do is put my baby in a chair (bouncy chair, infant car seat) and hold her hands in front of her and "pull" her forward. Most babies heads lag behind, meaning that as you are pulling them forward, their head is not aligned with their body. It lags behind..hopefully you understand what I'm saying. Anyway, I did this as a game a couple times a day until my baby's head / neck got strong enough to stay aligned with her body as I pulled her forward. You can also do this from lying down as well. Pull the baby up, hold his hands in front of him.
You really need to take this issue to your pediatrician and have your baby's mouth fully inspected. Amateur advice is not going to correct it, if it is in need of correction and the speech therapist told me that a clipping is so easy to do. Really, if you are not willing to do it for the sake of breastfeeding, then you need to consider how a tongue tie will affect his ability to move his mouth to learn to make sounds, which will affect his speech (think: delayed speech), and how he will be able to move his mouth to eat. IF your ped says it looks fine, suggest he/she refer you to a speech therapist anyway just to that you can get that reassurance a mother needs to know that her baby is really fine.