Mrs Stove swears by the Ergo baby carrier which is _much_ smaller and lighter than the metal framed equivalents. Its also suitable for very young babies and holds the child closer to your back so there’s less swinging around. In winter its much warmer, and since you’re in contact with the child its easier to tell if they’re comfortable/happy/asleep. It’s a rucsac style rather than sling, but can be configured for front or back.
Downsides are that its hotter in summer and has almost no additional carrying capacity (tho’ you can just wear a separate bumbag for that. There’s also no rain cover, the child would need to be in separate waterproofs (then again, we always had to do this anyway with the ‘proper’ baby carrier.
We’ve carried our kids from a few months up to age 3.5 in the ergo, and because its so small/light you can easily take it on a longer hike ‘just in case’.
New they are c. £60, I’d guess they’re around half that secondhand and easy to sell on if it doesn’t work for you.