i have an antique brass bed, in a guest room, with the same kind of side rails. i think they might be put in upside down (in the photo) and, therefore, are on the wrong side of the bed. my bed was put together like that by my last mover and was recently discovered by my daughter when she was here visiting. she wasn't able to get the mattress and springs off so just put short boards at the corners to keep them from falling off. i got new carpet since then and i asked the installers to put the rails on correctly when they reassembled the bed. sorry this is so long!..... i don't know if that was done or not and the bedroom is on a different level of the house than i am on and i am in a wheelchair so i can't go check. regarding the length of the mattress, yes, today's mattresses are too long. i bought a used one about 25 years ago, when i bought the bed, since it was shorter than new mattresses at that time. i hope this makes some sense!

If you have the room for it King is always better! But just keep in mind its always harder to downsize once you’re used to it. we upgraded from Queen to King when I was pregnant with my second kid.. i was already feeling cramped with one kid kicking me.. fast forward to now Ive separated/divorced and I let ex hubby keep King bed but i got myself a Cal King out of wanting to keep the space i was used to and my littlest still bed sharing… my current home has small bedrooms and i am now considering downgrading to a queen to have more room in my master bedroom, but i dont want to give up all the room.. wish i didnt get used to it now, because my bed takes up most of the room 😭

There are a few types of KD (knock down) connectors. I think the "cross dowels" are probably strongest for your application. Rockler also carries a variety of bed frame connectors for a stronger, but more permanent solution. Here is a link that might be useful: Connectors at Rockler

It might be just a matter of whether you like the oversize look, like in Jay's photo. OP: Do you share the bed? Are the two of you always fighting over the covers? Then maybe bigger is better. BUT--the flip side: In the winter months, I have a duvet that covers the side pieces of the bed, and I thought that would be good -- extra "blanketing"=extra warmth. Its a duvet for a smaller-size comforter. But it really does tend to overwhelm me, and the look of the bed. It's flannel, so I get overheated with that much more fabric. Also, it is a BEAR to shake that duvet out in the morning and get the inside comforter's bunched-up parts (on the sides) to get back to where they're supposed to be. There are devices to keep the corners in place (inside laces, velcro, inside buttons, et.), but not so much for the sides. The full-size duvet, for me, verges on the unmanageable to get it back in place, flat, to make the bed look nice again. (It also doesn't help that I have a ceiling fan above the bed--I've bumped it a few times!) So unless your husband/significant other usually helps you make the bed in the morning, that'd be something to think about. I think you have a lovely bed, beautiful wood, and I would want to see a bit of the side rails.