JP1 is the most flexible DIY platform that I'm aware of. There are over 100 models to choose from, and a few are similar to some old Prontos. And JP1 is so cheap, even if you try it and don't like it, you've lost virtually no money. I advise you to pick up a Nevo C2 for $16 from ebay, install Remote Master and give it a try. It has a nice mix of hard and soft buttons, nice ergonomics and a good LCD. You can even import all your old pronto hex codes if needed. If that's not enough customization, other screenless JP1 remotes have far more.