Help!?

I need a place for tall and skinny baby clothes...My son is 4 months old and is wearing 3-6/6-9 (25.5 inches) length depending on the brand and can still wear his newborn pants around his waist. Some of his 0-3 pants fit ok as well, but they all look like shorts on him. I can get one or two pairs of his 3-6 month pants to stay up (they have really good elastic in the waist) but they are still pretty big on him. Can anyone help? I really don't want to spend hours altering his clothes since he's going to grow out of them quickly. He grew out of his 0-3 at 2 months and he's almost out of his 3-6 at 4 months.