Hi and welcome to Sling Meet, it would be great to see you next week.
I don't have any of these two carriers and no experience with them but someone else might. But bring the Connecta, it's a very good carrier so maybe it just needs a bit of adjustment to make it comfortable for both of you.
I also have a curved spine so I'm really careful with my carriers or my back (and head and shoulders!

really hurt.
How old is your son?