You can use FingerTerm on Nokia N9, like I do. It isn't as good as a HW full keyboard, but it's the next best thing. Even more, it is also opensource.
Aegis security system is a bit more limiting than I would like it to be, but you can easily bypass the limitations with inception (for the moment the site seems to be down, so just use your favorite search engine to get some info). With inception you don't even need a computer, everything is done on the phone afaik. Haven't yet tried it myself, because so far I am fully satisfied with the official "developer mode" which can be easily activated from settings menu.
One extra feature for N9 is the community backing it up. You can join IRC freenode network and join #harmattan channel for instance and get help in matters related to SW development.
An alternative would be to try to find a Nokia N950, but as I recall although it has a full hw keyboard, it has some drawbacks compared to N9.
Finally I must also add that as far as I can tell you can't get a better user experience than with N9 UI. It's simply amazing. I hope Jolla will be able to provide it in their future phones.