I plan to travel from Brighton to London on the next two weekends. I've done the journey before, though now I live in - Hove, actually 
As far as I can see there is still a Thameslink only ticket for this route, costing £8.70 return with a Network Railcard. My terminus would be London Bridge (though I'm flexible). This is valid Sat/Sun & none of the time restrictions I see on brfares seem to be of any concern (I will be arriving in London around 10am, leaving around 8pm) (there are other regular ticket options valid also on southern at £17.40, and which I could take from my closest station, Portslade)
However, none of network rail app, thameslink website, train pal, seem to list this thameslink only ticket.
From memory it's easy/quick to get at a station with machines (or office) so I plan to visit prior to my trip(s) -- and also see if plusBus is valid to add. Shame that isn't eticketable yet
I may also get a ticket portslade<->Brighton return instead). I've not
done this journey for a year or two now though, so perhaps something's changed?
Any ideas on whether the base train ticket can be bought online? Any sites better at this, or tricks? I presume plusBus can't yet?
Or have I been caught out by misunderstanding the ticket validity

As far as I can see there is still a Thameslink only ticket for this route, costing £8.70 return with a Network Railcard. My terminus would be London Bridge (though I'm flexible). This is valid Sat/Sun & none of the time restrictions I see on brfares seem to be of any concern (I will be arriving in London around 10am, leaving around 8pm) (there are other regular ticket options valid also on southern at £17.40, and which I could take from my closest station, Portslade)
However, none of network rail app, thameslink website, train pal, seem to list this thameslink only ticket.
From memory it's easy/quick to get at a station with machines (or office) so I plan to visit prior to my trip(s) -- and also see if plusBus is valid to add. Shame that isn't eticketable yet

done this journey for a year or two now though, so perhaps something's changed?
Any ideas on whether the base train ticket can be bought online? Any sites better at this, or tricks? I presume plusBus can't yet?
Or have I been caught out by misunderstanding the ticket validity