For clarity, it's 3 to 6 players including the game master.
However, I don't think you'd need to change/adapt much to play 1-to-1 (2 players including GM) .
You'd need to pick three to four Joy in Small Things objects. Normally, each player receives one from each other player. In 1-to-1, the GM and the player would each choose up to two objects.
Some moves, ask the player to designate another player to write a Talk of the Moment. This distributes the creative load and enables a smoother story progression but it shouldn't be too much of problem for a single player to designate themselves.
I'd recommend to lower mysteries complexity ratings (as I do for shorter sessions and as demonstrated in the Replay) and to pick the shortest of the three proposed Rumors Mill.
Please let me know how your 1-to-1 experiment goes.
:)