Hi there,
Congratulations on your impending arrival!
I too was given 2 secondhand Baby Bjorns when my little one along. When she was tiny it was fine, and she enjoyed looking out... but I didn't rate it overall. I bought an Ergo and absolutely LOVED it. I was still carrying her (commuting for nearly an hour to CJ) until she was 18m+. And she was a chunky monkey. If I have another one I will buy the baby insert and use from birth - I can't tell you how much I love it - so comfy, and totally washable.
I think I've heard that you can breastfeed using some slings, but despite being a merry out and about breastfeeder i couldn't imagine it working for me.
Try
http://www.bigmamaslings.co.uk/zen-cart/index.php for advice on which sling to buy.
Enjoy!