Hello Soangoidaing97
As general advice from me, having worked as a flight attendant for ten years: travel light, it will definitely ease your travel, also in SBB and other trains. Rather, opt to wash your clothes while travelling.
Instead of the Bernina Express, you could take any train serving the route from Chur to Tirano, requiring a change, though. All trains from Chur to Tirano take the same route as the Bernina Express. The advantage of the Bernina Express is, it has a documentary that provides some insights on the landscape you are travelling in.
Sending the luggage might not be doable as it takes too long for the luggage to arrive.
Kind regards,
Roland