I used a sling quite a lot, but like you, realise that that there have been a lot of developments. Daughter and dil were both keen sling users, and from their experiences, it seems that some types are suited to small babies - particularly Moby wrap. That type would probably do for first few months, and I wouldn't suggest getting other one at this stage - it's better to to wait till baby is ready for bigger size before investigating the more expensive ones.
Like muffin, I would suggest looking at sling libraries. My daughter used one of these and was able to try a few slings with her baby for a few weeks before deciding to buy. Trying a few in a shop isn't the same.