The most useful term is one of those you already mentioned: non-trinitarian.
The technically correct—but practically speaking useless—term is unnitarian. As you already found out, the latter quickly becomes confusing due to its overlap with a specific denomination that has other theological (in)distinctives. There is one more related term, Arianism, which is particularly useful in tracing references to various groups that have denied the divinity of Jesus. You will usually find this term used in the context of identifying sects that differ from orthodox doctrine in not acknowledging the divinity of Christ.
Even armed with the 'right' terms, I am afraid your search may prove harder than you expect. I will take the liberty of suggesting a few reasons why this hunt will be difficult:
What you describe as your target does not exist.
To my knowledge there is no group that matches the criteria you set out. The long tail of non-trinitarian sects only gets farther off center from the ones you identify as "radically divergent".
Even theoretically speaking, it could not tenably exist.
If you are going to build a faith around a non-trinitarian version of God you are going to have to de something with the Bible. Either you discard it entirely or you give it a makeover. In order to write Christ's divinity out of the NT, you will have to take such liberties in interpretation that you no will have any reason to believe much of the rest of it. The foundation will be so moved that any cohesive structure you build on top of it will by necessity bear little resemblance to Christianity.
This latter route has of course been tried. It is a well traveled road. Most of those who have traveled it historically take the form of 'reconstructionist' sects—Jehovah's Witnesses and Mormons being the best known examples. The former believes Jesus to be more angelic than divine (or human) and redefines the role of 'Messiah'. The latter completely redefines the nature of divinity such that humans can become god(s).
Alternatively there are some less well known 'renewal' sects that take a slightly different tact*. The one that comes to mind as non-trinitarian is Oneness Pentecostalism.
Finally, whatever you look for, remember in the end you are not looking for what suits you but for what is true no matter how much it might not suit you.
* For info on how this is different see What is the difference between the Jehovah Witnesses and Pentecostal Churches?, but note that general Pentecostalism it Trinatarian so that question is only useful for understanding the relation of reconstuctionist vs. renewal sects is. Oneness Pentacostal are a subset of with several extra distinctives including-rather excluding- trinatarianism.