It is often said that the knight has five good levels: 1st, 2nd, 3rd, 4th and 20th. Basically, nothing in the class from 5 to 19 is very good. Loyal beyond death is unbelievablebut you will spend 16 class levels getting it, so keep that in mind.
In the end, since hunter and knight are so similar, this question on a hunting tank is a very good read. Since you are not a fighter and you do not get nearly as many extra feats (or such quality), you can not do everything mentioned in the answers, but as the suggestions relate only to feats and objects you have these options and possibilities. just choose less. Dungeoncrashing is out, but it also allows you to skip the options related to Bull Rush; Opportunity, stumble and intimidation attacks all remain strong suggestions for you.
In particular, since the best thing you shoot from increasing the number of knights is an increased backup throw for DCs. courage testyou should probably look into this and pump the charisma, which also improves bullying. You do not get the quick intimidation of a Zhentarim soldier, but the formidable property of the armor of Drow of the Underdark can let you do it as a movement action. Combine that with the skill trick Never outnumbered Complete scoundrel and the feat of imperious command, also of Drow of the Underdark, and you can reduce everyone around you to shake at the start of each fight, while simultaneously challenging them to a courage test so even if they do, they still have to fight you. And you would always have your usual action to attack someone if you wanted it.
Another potential use of charisma is the use of the magical device: you can make it a class skill by exploiting the exploit of an apprentice. Player's Handbook II. If your first game in combat is to intimidate everyone around you, courage test them and also activate a useful rod, you are in serious business. Most of the time, you will probably have to put yourself in the place, but it is worth having the option.
Unfortunately, Intimidate and courage test are effects affecting the mind (well, probably), which means that if you fight constructions, undead and similar blind creatures, you could be effectively canceled. It is there that intervene trips and attacks of opportunities. Unfortunately, as a pure knight, you have to call on the combat expertise to get an improved trip, which means Int 13, which hurts a lot when you want to emphasize the charisma and the Constitution. Dexterity not bad. You will probably have to empty your Force, which means that you will probably want Weapon Finesse (or a Feycraft weapon) – ask your DM if non-light weapons that work with Weapon Finesse can take advantage of Feycraft in the same way as weapons light!). You could try to be a killoren from dragon Nature Races (dragonborn is a model, which means you also get a race to accompany it) to take on Charming the Arrow: you can actually use it in melee with any of the hybrid arcs of Nature Racesbut it's probably not worth giving up.
The suggestions of Mage Slayer, Occult Opportunist and Supernatural Instincts recommended for the hunting tank are also good options for a knight. The exploits of Close-Quarters are probably too situational to be bored when you do not have so many bonus explosions. Martial study and martial posture of Battle Tome are also good ideas – you probably want defensive reprimandand you really want stuffed with blades. Island of the blades and iron guard It would be good too, but you only have one position at a time, so be aware of it.
Finally, at very high levels, you may want to buy a starmantle coat of Book of exalted acts. Non-magic weapons that hit you while you wear them disintegrate. If you can dispel the creature's equipment – there are weapons properties in Compendium of magic objects doing exactly that, or spell-casting allies can help, you can destroy everything. However, it weighs 132,000 inches, can destroy your loot and can spoil the fun of meetings, so think about it and maybe run it through your DM and your group before doing it.