As in many things: its more complicated.
The problem starts with TPE vs silicone vs Skin. Skin has a very diffirent texture. Skin is both very smooth, yet also rough. Its smooth by default because a tiny layer of moisture helps lubricating it, which is why you can often slide with skin contact. TPE is sticky on the other hand which makes this sliding not happen.
TPE requires lubricating before it becomes a bit smooth, yet nearly always you will need more lubricant than skin would. This is why TPE textures are often very uneven, without it it would be too smooth.
There is also the part of heat. its very hard to mimic realistic body heat. Just a fleshlight being warm wont do it, as a human keeps adding heat, yet a fleshlight will cool. A heating sleeve can work, but its on that often going to heat the entire sleeve, and is on that if you want realism a must. Pre-heating tools wont work, the sleeve cools too quickly.
Its also lubrication balance. A women creates lubricant by arousal. If the stimulation is low, not a lot will be added which in turn increases the sensation by providing more resistance. The more aroused she gets, the more she will create lubricant, but she will also tighten equaly with it. This is for a fleshlight impossible to mimic currently.
Pressure systems are the hardest parts to mimic, as keep in mind that women can squeeze a lot. And even the heartbeat can be felt through it sometimes.
A fleshlight is competing with thousands of years of evolution. Its unreasonable to ask the same of it. Trying to get as close as possible is best. But the problem here is: no one is the same.
And this is why even very textured fleshlight sleeves can often do the job fine. TPE can squeeze a lot, and its tightness and texture combined define how you feel it. But very often its near impossible to feel the exact texture, you can distinguish regions well, but if you wouldnt know the internal texture and tried a new unknown fleshlight, you would have no idea what texture it would be. You just arent sensitive enough for it, and never will.
But this is a benefit!
Because you barely can feel the exact textures, the most strange patterns they used will often end up giving a notable enough diffirence, a diffirence that also happens between diffirent women. This makes most sleeves of any toy end up more realistic in feel compared to how they truly are.
Find a sleeve that tries to mimic things you like (tightness, roughness, or open sections). And most of the search is already done. The exact texture is rarely relevant. Its only relevant for someone that is nearly exclusively using fleshlights and wants to feel variety between those. And yes, extensive fleshlight use will give this capability.
But realisticly, most men will never experience that. Just like in a relationship you are fucking the same women for an extended period.
Just find 1 good sleeve that you like, and you are generaly settled. No matter how unrealistic it is, if you like a sleeve, its a good one. Online reviews are completely pointless on that.
For fleshlights, its most important how sensitive you are, the more sensitive you are, the smoother you want your sleeve. But if you arent sensitive, go for a rough sleeve, its far more likely to feel realistic, because you actualy feel texture.
Sadly, this means you most of the time will have to try several fleshlights before you find one you like, but thats just how it is. Some tools can help, but most of the time you still will need some reference points.
So my recommendation is to take a sleeve that is deemed a bit wide, but heavily textured. These are the so called ‘average intensity’ ones. They set a base line for many things, and most notible: texture and tightness. Does it stimulate enough? search similar. is it too much? search smoother. Do you not feel texture? go for both tigher and more textured (both, so the next time you ensure you can feel diffirent sections).
Its sadly a bit of an expensive search. But at the same time, a sleeve variety can help spicing things up based on the mood.