The phrase "almost the only form" is correct and usable in written English.
It can be used to indicate that something is one of very few forms or types available, but not the sole one.
Example: "In this region, almost the only form of transportation is by bicycle."
Alternatives: "nearly the sole type" or "practically the only kind".
Individualism is almost the only form of active opposition the citizenry has left at its disposal.
In writing, it is almost the only form used (except for limited printings of dialect literature); in speech, it is the first or second language of virtually the entire population.
With no schools to teach the literary language nor any native nobility to support the literati who used it, the dialects appeared for the first time and began to be written in the paper manuscripts that constituted almost the only form of publishing available to those using Irish.
Under the later Seljuqs (particularly the Artuqid atabegs of Mosul) and the Mamlūks, engraving became almost the only form of decoration, but only to serve as a basis for the yet richer technique of inlaying, or damascening: small silver plates and wires, themselves delicately engraved, were hammered into the ribs and surfaces, which were hollowed out and undercut at the edges.
While swimming, the woman felt that she could use her body as she did before her pregnancy - as almost the only form of exercise to do so.
Juvenile ravens are driven away from carcasses (in winter, almost the only form of nutrition) by mature mated pairs, but (apparently by exchanging information in nightly roosts) the former often manage to recruit sufficient numbers to drive the latter off.
"They are particularly important as they are almost always the only form of retail provision in the settlement in which they are based, particularly those in more isolated parts of the UK and particularly so for the elderly and less mobile," Alcock adds.
Bufo siculus almost never shows a reddish-orange coloration, characteristic of many B. balearicus, the only form of the subgroup with which it may co-occur on Sicily.
Augustus Pugin even pronounced that medieval architecture was the only form suitable for a church and that Palladianism was almost heretical.
