That's a really tiny baby to make a decision about any SSC, at that age I'm usually still wrapping with a Moby or maybe tucking them in a ring sling. I don't break out the SSCs until they are older.
I don't nurse in any SSC though- so I'm not a lot of help there, if I want to nurse and carry, my go to is a ring sling. I just can't pull it off with anything else.
What I have discovered with my SSCs is that they really are more comfortable when they are sized. A Beco would work for a few months, but after 15 months or so (or even earlier sometimes) I want a toddler carrier with a greater width and a nice high back. My nearly 2yo is usually worn in our toddler Kindercarry- and it's SO much more comfortable for both of us than most of the others. My three year old is carried in a very large preschool sized carrier I made just for him a few months ago.
You can always use the carrier for a while then try to trade it on TBW if you find you still aren't loving it once your lo is big enough to be legs out. (It may be that he is ready for legs out with the Y panel now, that could make all the difference in comfort now.)
I would have loved the Y panel when I was first learning back carries, but that stage only lasted a couple weeks and now I just pop DS in on my hip and spin him around to the back, the Y panel would just get in the way and annoy me.