It is often said that the knight has five good levels: 1st, 2nd, 3rd, 4th and 20th. Basically nothing in class from 5 to 19 is very good. Loyal to death is amazing, but you will spend 16 levels of class in getting it, so keep that in mind.
Ultimately, because the fighter and the knight are so similar, this question about a combat tank is very good reading. Since you're not a fighter, and you do not get nearly as many bonus feats (or such high quality), you can not do everything that is mentioned in the answers, but since the suggestions are mostly just feats and objects, you have those options and you just have to choose less of them. Dungeoncrashing is out, but that also allows you to ignore options related to bull rush; Attacks of opportunity, shooting and Intimidation remain solid suggestions for you.
In particular, since the best that can be obtained from Knight's high levels is an increased Salvation CD for temper testYou should probably lean on that and pump Charisma, and that also improves Intimidate. You do not get the quick-acting Intimacy that a Zhentarim soldier does, but the fearsome property of the armor of Drow of the Underdark It can allow you to do it as a movement action. Combine that with the skill trick of Never again outnumbered Complete scoundrel and the Imperious Command feat, also from Drow of the Underdark, and can reduce all those around him to cuddle at the beginning of each fight, while at the same time challenging them to a temper test So even if they get over it, they still have to fight with you. And you would still have your standard action to attack someone if you wanted.
Another potential use for Charisma is to use the Magic Device, which you can do a class skill by taking the Apprentice dowry. Player's Manual II. If your opening gambit in combat is intimidating everyone around you, temper test they and also activate some useful wand, you are in serious business. Most of the time you probably have to move to a position, but it's worth having the option.
Unfortunately, both Intimidate and temper test they are effects that affect the mind (well, probably), which means that if you are fighting against constructs, undead and similar nonsensical creatures, you could be effectively annulled. That's where the shots and opportunities attacks should appear. Unfortunately, as a pure gentleman, you have to take advantage of the Combat Experience to get an Improved Journey, and that means Int 13, which hurts a lot when you want to focus on the Charisma and the Constitution, and the dexterity is not bad. It is likely that you will have to download Force, which means that you probably want a Weapons Finesse (or a Feycraft weapon, ask your DM if non-light weapons that still work with the Weapons Finesse can benefit from Feycraft as they do). light weapons). You could try being a dragon-born killoren from Races of the wild (dragonborn is a template, which means you also have a race to go with it) to take Charming the Arrow: you can use it in hand-to-hand with one of the hybrid arcs of Races of the wild, but probably it's not worth giving up the scope.
The suggestions of Mage Slayer, Occult Oportunist and Supernatural Instincts recommended for the combat tank are also good options for a gentleman. It is likely that the dowries in the closed rooms are too situational to bother you when you do not have so many additional dowries. Martial study and martial posture Battle volume They are also good ideas, you probably want defensive reprimandand you definitely want scrub of blades. Island of blades Y glow of the iron guard It would be good too, but you only get one position at a time, so be aware of that.
Finally, at very high levels, you may want to buy a starmantle cape since Book of exalted works. Non-magical weapons that hit you while you get disintegrated. If you can dispel the team of the creatures, there are properties of weapons in Compendium of Magical Objects to do just that, or the spell allies can help, you can destroy everything. However, on the other hand, it is 132,000 gp, potentially destroying your booty and can ruin the fun of the matches, so think about it and maybe execute it with your DM and your group before doing it.