You need 42" aisles all around. Measure out 45" from your existing cabinet boxes and put down blue tape. All the way around the room. That's what size island is possible.The 1 1/2 counter overhang on both the perimeter and island will swallow up that ''extra'' 3".

Most kitchens without islands don't have them because there isn't room for them.

life is rarely ideal, you can cheat down to 39" on a short side if there arent fridge doors or dishwasher to open and generally only one cook is in the space. but leave a lot of space on the other side of the island (away from the main kitchen) to move large things through the space.