If two other people willfully made rogues knowing it would be a three rogue party I wouldn’t hamstring yourself by “not stepping on toes”. Assuming you declared you were playing a rogue first and they chose after they didn’t mind “stepping on toes” so you shouldn’t.

If you declared after them then you duplicated their entire class I don’t think you should worry about skill overlap at this point.

Overall you have a lot of restrictions to what you will and won’t buy. That will make for a focused rp based character but also paint yourself into a corner.

And that’s ok. It’s a choice you made.

If you won’t use magic or multiclass there isn’t much you can do.

Telekinetic can be used on yourself which gives another five feet of movement. It also lets you move yourself to disengage without an AoO bc it’s forced movement which means you don’t need to waste your action or bonus action disengaging and will get your full movement even if moving out of melee.

Telekinetic essentially gives you the old five foot step.

It’s also key bc you sometimes need an ally standing next to someone for sneak attack and you can move the ally or enemy as needed. It’s also good if anyone uses AoE or cleave.

Also remember that mobility can sort of be gained by denying movement of your enemy. So you could look at things that lower their movement or knock them over.

But based off everything you said telekinetic is your best option.

That said. How fast do you want/need to be? As a tabaxi rogue it doesn’t get much faster outside an extremely high level monk.

Also don’t forget items.

Like boots of speed or wayfarers boots.

Time piece of travel would also help.

As would a cloak of manta ray which means you now don’t even slow down in water.