Constipation transitioning milk at 1yo

Hi all! My 1yo 2m+ was fully bf until his 13th month. My supply started to drop afterwards, so I mix fresh milk and my bf. Started at a ratio of 80:20 and now about 70:30 or 60:40, depending on my supply. Initially he seems to be all good but in recent weeks I noticed his stool is getting harder. He also seems to be having constipation on some days. Some days he passes out hard stool of his fist size, some days he looks constipated with no stool out. He's eating well in the day, but he doesn't drink as much water as he should I think? His weight is about 11kg, but he drinks only 100-150ml, is that normal? Tried to change cups/ bottles also, so the water intake amount varies each day. Tried greek yoghurt and many fruits. Papaya, banana, watermelon, apple, grapes. I've also tried to rub oils and balms on his tummy, back, sole etc. Tried honey water and watermelon juice too recently. Dipped him in warm water too and let him play about 10 mins during shower. Still the same. Can share how you all deal with this? For the record, I'm using uht fresh milk. A personal preference but trying not to use formula as I'm feeding him well (he's eating well too) so I believe the nutrients are better from real food.#pleasehelp #advicepls