I bought a Croozer trailer and have been very impressed with it. It doesn’t have any suspension, but this hasn’t been an issue on road or gravel tracks. It’s very light, can be easily converted into a stroller/jogger, and easily attaches to the bike. I haven’t used it with a road bike, only a hardtail mountain bike. I don’t know if you can get attachments for non-QR axles, and I think I’d be a little wary of the stress it could put on a carbon frame (although this is probably in my head). If memory serves me correctly, we started using it when our son was around 15 months old but we could have started earlier if we’d bought an infant sling. We’ve only got a single-seater, but it’s still pretty large when folded and with wheels removed, and can be a bit of a pain to try and fit in with other luggage when going on holiday.