@georgina I haven't heard 'onboard' as a verb, so perhaps "...schedules to welcome me onboard."
However, the Brits often understate things, so the following might be quite enough:
Just a note to say thank you for having me.
You could add: "and making me feel welcome/at home" but there again Brits stereotypically do not mention "feelings"....
Try googling "very British problems" such as:
A: Sorry, did you say something?
B: Sorry, did I?
A: Sorry, I thought you did.
B: Sorry, I really didn't mean to.
A: That's okay, no need to apologize.
B: Sorry, won't happen again.
....