Baby slings are amazing and a very safe and healthy way to carry your baby. We personally used a Karyme wrap which was super cosy and very easy to tie, but now as my daughter has got older (17 months now) I find the mei tai easier for putting on my back. Its really all down to personal choice.
I suggest perhaps going on www.naturalmamas.co.uk and asking around there, some very good advice on that site. Also I found my local sling meet on NaturalMama's which was a place to meet like minded mums and also the organisers usually have a number of slings for you to try before you buy.
Hope that was helpful.