A little update to announce that my quest is at an end.
My dilemma began with the choice of TS9 vs TS808, and it ended on that theme without me having to make a decision. I was fortunate enough to stumble across a (very cheap) Chinese clone called the "Tubescreamer Demon" - same controls as a regular TS (Drive, Tone, Level) plus a toggle switch to flick betwen TS9 and TS808 modes.
In short, both circuits in one pedal, for a fraction of the price. I'm sure the audiophiles will be able to play with it and tell me where it's lacking over the original Ibanez pedal(s), but it does the job as far as my ear can tell.
The only drawback is that they labelled all the controls in Comic Sans...