I don't think a bjorn would be the best thing for you as you would only be able to use it for around 6 months with the new one before it would hurt you to carry him. They are also possibly bad for baby's spine as he would be dangling from his crotch - in a carrier a baby should be sat as in a seat with their knees higher than their hips which is how they naturally sit when you cuddle them. If you buy a better designed carrier you will easily be able to carry both your boys for years. It would be worth having a look at the babywearing sticky viewtopic.php?f=36&t=98827 for ideas and advice. What is perfect for one person is not necessarily perfect for another - partly because we are all different shapes and sizes and partly because we have different ideas of what makes a carrier best.
I have an awful lot of slings
Our most used one is a connecta as that is OH's carrier, he doesn't like having to tie things, he prefers buckles. I bought it when she was 6 weeks old so it is definately suitable from birth to toddler. We have a solarweave one for summer and it folds down so small! Our friends all bought the Tomy or Bjorn or other types that Mothercare had in stock and by 6 or 7 months couldn't use them any more as they pull on your back and are sore for you to use. Even though I have a dodgy pelvis I could use the connecta to very comfortably carry our nephew who is 20 months and very tall.
My favourite is a mei tai made by Ocah. The one I have is called a hybrid. As I said, I have a dodgy pelvis so I really feel when I am carrying if a carrier is not supportive enough and I can't carry my daughter in my arms for more than a couple of minutes. I can carry her in this for hours! I think it may have been a bit big for her as a baby, she may have been drowned in it (though perfectly safe). We got it when she was 5 months old. She does have a waiting list though.
I barely used stretchy wraps because I bought a Moby and it is really thick. DD was born in May so by the time it was cool enough to use the Moby I had bought woven wraps and preferred the support. I leant slings to a friend and she had a stretchy wrap that she loved when her daughter was new but when she tried one of my woven ones when her DD was 3 months old she found that far more supportive. Woven wraps are so snuggly and great for learning on but like the bjorn they aren't supportive enough for your full comfort after 6 months.
Woven wraps have a learning curve but I just practised while baby was asleep. If you have a mirror you can practise in front of it's fine. I use woven wraps when I am going to be taking DD in and out of the carrier a lot as I find that easier with a wrap. They are very versatile and I love them! The Ocah is the only carrier I have tried that is more comfortable than a wrap. I haven't tried all the brands of mei tai out there though.
Buying 2nd hand would make the initial outlay smaller and then you can sell the sling on later. 99 out of 100 of the slings on ebay are not supportive enough and that is why there are so many there. I have bought and sold second hand on babywearing websites and these are also good places for more sling advice. For example, if you choose to get a woven wrap you will find there are an awful lot to choose from!
The first thing to decide is whether you would prefer a carrier with buckles or not. The advantage of wraps and mei tais is that because you tie them you can get them to fit the 2 of you perfectly. Buckle carriers don't have as much adjustablilty but many people don't want to tie. Also if you put on a wrap outside in winter it is very hard to keep the ends clean. Have a think and then ask any more questions you think of. Perhaps you should have a look on a babywearing site for more detailed information about lots of different carriers.
Dunno if that comes into the equation or not but felt it worth mentioning!!!
