Paint texture getting rough at second coat
Your roller seems very small for painting a wall. 1cm - 3/8 would work well for touching-up. Perhaps you should try a 2-3 inch roller, this would be much quicker, be more consistent and you’d be using the same tool as a professional would use. Additionally, if the paint you’ve used is old or been allowed to lose moisture it may be thicker than when new. As your paint is water-based, adding a small amount of water may help (try on a small area first). You also mention about bubbles and being ‘light with the roller’. Emulsioning can create tiny bubbles as the roller passes over the surface but theses will quickly disappear. As for being ‘light’, there shouldn’t be a requirement to be light with the roller to get a good finish. Buy a quality shirt-pile mohair roller for silk emulsion and a medium-pile sheepskin roller for Matt emulsion, avoid spongy foam rollers and you’ll be painting like a professional!