I've found one which is really simply because uses Youtube content and there is no need to switch between Youtube and downloader https://y2bee.com free a little bit annoying but simply and fast
I also use the downloader snaptupe app download from Youtube, where there is no need to copy the url from Youtube, on the page in the browser window enter the song title we are interested in, then choose the format to convert and download the mp3 file, nothing simpler