The suggestion I've encountered is that the manned CCV component is likely to be executed as a further development of the Type 31 frigate, i.e. significantly scaled back relative to the previously mooted Type 83 destroyer.
The language of "at least six" new CCVs should also be considered in context. Replacing the Type 45 destroyers at least one-for-one sounds well and good, until one considers that the Type 45 program was originally intended to deliver twelve destroyers before it was cut back to eight, and then six. Six downscaled CCVs would represent a further decline in the inventory, just as the transition from the originally envisioned thirteen Type 26 frigates (to replace thirteen Type 23 frigates, down from the sixteen that entered service before three were sold to Chile) down to eight plus five cheaper Type 31 frigates was. The roadmap is consistently in the direction of decline, with the only reversal of note being the alleged commitment to "up to" (note that language) twelve future SSNs. But crucially, this decline is no longer occurring in the context of the post-Cold War peace dividend or even the Global War on Terror. Rather, it is occurring in the context of an alleged, officially accepted era of renewed peer threats.
The British government has publicly committed to increasing defence spending to 3.5% of GDP within the next decade. Yet despite this, former Defence Secretary John Healey resigned in part over Starmer's refusal to plot a budgetary path for defence spending to reach even 3% of GDP. Current plans have defence spending rising from the current 2.6% of GDP to 2.7% by 2030. Achieving 3.5% of GDP by 2035 will therefore require very significant and rapid increases to be delivered by a future government. Even if this were to miraculously occur, rapid budgetary increases are difficult to absorb efficiently, and the fruits of those investments are of course considerably delayed. From a mundane, defence-of-the-realm perspective, if 3.5% is believed to be an appropriate target then a gradual and sustained rate of increase is the most sensible route to achieving it.
Of course, the reality of the situation is that, public statements notwithstanding, the British government clearly does not actually believe that there is a credible near- or even medium-term Russian threat, and it has no intention of actually delivering the increased defence spending that it has publicly committed itself to. The gap between rhetoric and commitment has been safely filed away as Somebody Else's Problem -- with Keir Starmer's political demise and imminent replacement by Andy Burnham, now quite literally.