There are sleepers from Bucharest or Sofia to Istanbul in June, but I think there’s nothing between Budapest and Sofia at the moment (there are no trains at all between Budapest and Belgrade).

There’s a good write up here.

https://www.seat61.com/Turkey.htm

In summary, I think you’d need to travel Budapest to Bucharest overnight, then wait nearly 24 hours, then Bucharest-Istanbul overnight again.

Budapest to Sofia is a slow journey with a few stops, one being quite long. However, that’s not so bad if it’s the only way, it goes Budapest to Craiova to Vidin to Sophia, taking 26 hours.

It looks like we can then get the Bucharest to Istanbul sleeper from there - although it doesn’t come up in the timetable searches, the only train stops at KAPIKULE but I think that might be the border crossing? sedit] I don’t think this is the sleeper as there are no reservations, so still not sure where the sleeper availability is.

Anyway, we’ll get there!

Also, thank @ralderton for the link. It’s a useful site but like many of these sites, none of the updates/posts are dated so I have no clue if I am reading something one week old or one year old, so I don’t rely on them.

He updates his site frequently, so it’s pretty good information. Although there’s always changes and track work that can change things.

Here's the actual timetable to Istanbul from a official source:

https://p.bdz.bg/www/s/o/sofia-halkali-27032023-1-3707.pdf

But the one for June is not confirmed yet, but may be similar.

That’s great. I think that’s the reason - no timetable yet. So I will keep an eye out. 

I’ve booked everything from London through to Budapest - just that last bit to do! 

Thank you for your help.