I had a hot sling for my baby when he was little and it was great for nursing and would let me get adjusted with both hands! As he got more mobile, I felt like the material would stretch out too much and moved over to a mei tai. I got an Angelpack off Ebay for $30. They tie around your waist and over your shoulders. I keep it in my car and use it almost every day because my 11 month old has been 20+lbs since he was about 6months old and gets very heavy. It's also easier in the grocery store, Target, etc., especially when I just want to get in and get out.
There are a couple other brands like Ergo and Beco that have buckles. I think the Angelpack does too. Buckles are great and worth the price because you can use it until your babe is a toddler! It's a great investment and the resale value is about the same.