Most of your requirements depend on the quality of each particular workplace; the only aspect that is susceptible to advice is the alignment between somewhat re

Most of your requirements depend on the quality of each particular workplace; the only aspect that is susceptible to advice is the alignment between somewhat relaxed environment, more or less Android and web for technology, and hard technical problems. For that, I suggest companies that are as small as possible (you would be more of a generalist and less of a cog), established (filtering out bad ideas and incompetent teams, and ensuring the time to reach a high competence level), product-oriented (to work on interesting improvements, customizations, support requests of something you can become an expert of, instead of random low quality consultancy projects). As specific examples: machines of all sorts (likely computer-controlled and with external management apps and other auxiliary software) or business software at the intermediate scale at which customers are many enough to ensure stability and variety, but large enough to need interesting kinds of individual attention.