For cleaning the sofa, I would rather recommend a hand hoover with a motorised brush head for a textile material. For stubborn stains, soak in advance with a microfibre cloth and distilled water. Dabbing is better than scrubbing. If necessary, use textile cleaner for sofa/carpet, but test first on a concealed area.
For a (synthetic) leather sofa, only use water and a cotton cloth, if necessary seal with leather care afterwards.
I don't recommend the Kärcher because it works with steam and pressure and the material of the sofa will be destroyed rather than cleaned.