TuYe R6.5 Sidewall Ultra Light Inflatable Sleeping Pad

Just from my experience longitudinal baffles are way more comfy as a side sleeper so the Flextail might be the better choice.

The sizing on the 6.5 is definitely smaller than advertised. I got the large one, which is in reality 188cm long and 62cm wide. About 8cm thick as well

I have the naturehike r6.5 pad, got it second hand and while it is fine, i wouldnt pay a 100e for it, as it doesnt have any warranty. The valve especially is not very convincing on these naturehike/light tour etc mats. I would probably try out the Robens Heatcore, looks like its right around 100 euros

I haven't tried the 5.8R but I would go for the R6.5 instead. 490g in regular size which is functionally a wide pad. The side wall construction is fantastic for edging and the baffling has fewer weld points with no disadvantages. Comfier than a Tensor or STS XR, but haven't tested the R rating yet

Flextail will be more durable and comfortable.

I actually just bought a naturehike Ultralight 6.5R sleeping pad to try. Definitely warm, lives up to the R value but for comfort wasn't as good as my Flextail Zero 6.0R pad, also very slippery in the tent but that can be fixed with some silicone dots. Overall wouldn't be bad as a starter pad but wasn't my cup of tea. FYI - sleeping pads, sleeping bags or quilts and a comfortable pack are VITAL to enjoying backpacking but there are good budget options for all. Also, check out the Sensory4U sleeping quilt on Amazon - $130 and it's a 850 down quilt, very light and warm. There are a ton of YouTube channels that talk about good budget gear to start with as well. Try Dose of Dirt, StepMassive, MyLifeOutdoors, or Dan Becker for good info on gear Darwin on theTrail, Homemade Waderlust, JupiterHikes or Oscar Hikes for good hiking info and tips as well.