If the paladin is the one focused on doing damage, you'll probably want to be looking at more of the tactical side of things, which might mean being a meat shield or just tripping stuff up and moving them around.
Given that you might have access to Enlarge person, being a big annoying target is probably your main goal. Depending on what counts as core, the
Stand Still feat from the SRD might work for you to keep your enemies from moving. Also from the SRD is
Knock-down which would help if you're going for more tripping options. Both would work nicely with
Combat Reflexes.
Shock Trooper is great for both offense and tactical defense since you can do a lot of damage on a charge, or you can opt to bull rush stuff around and perhaps even effectively trip them if you bull rush one foe into another.
Combat Brute might have more of an opportunity cost than you'd be willing to take even though it can combo exceptionally well with Shock Trooper. The
Knockback feat is the big (pun intended) way fighters can move stuff around and benefit from ST and CB.
Given all the feats you want you'll probably want to be human. That'll also mean you won't get a hit to your charisma or constitution. Although, upon looking at your con in the first place, it seems you probably shouldn't be the guy in the middle of everything...
Have you ever heard of the Horizon Tripper build? The original build is barbarian 1/fighter 1/ranger 3/Horizon Walker 6+ (to get the Shifting planar terrain mastery which allows from Dimension Door every 1d4 rounds). It might be adaptable for you if you plan on being more of the tactician so you can reposition yourself without actually having to move.
Improved Initiative is almost always good, and would allow you to get where you need to first before your partymates (and enemies!) do their thing.
Elusive Target is unfortunately quite feat intensive for what it does and isn't used unless dodge and mobility are needed for other stuff as well (mostly PrCs, though a couple feats are worth it as well). If it just required dodge, or you're able to get mobility for free (and by free I mean that it doesn't replace another feat that you might have taken) then it'd be worth it.