Not sure about the original key, but I play it in E.

E          C#m  B
How many fantasies
Were interrupted by
A hundred galaxies
That were drifting by

A                C#m       B
The Mona Lisa's got you in awe
The Mona Lisa's got you in awe
The Mona Lisa's got you in awe
The Mona Lisa's got you in awe

E          C#m  B
How many apologies
Were interrupted by
Learning how to read
Looking at the sky

A                C#m       B
The Mona Lisa's got you in awe
The Mona Lisa's got you in awe
The Mona Lisa's got you in awe
The Mona Lisa's got you in awe

C#m              E
Your baby's sleeping, sleeping
Your baby's sleeping, sleeping
Your baby's sleeping, sleeping
Your baby's sleeping, sleeping
Sleeping, sleeping
Sleeping, sleeping...

Your baby's sleeping, sleeping
Your baby's sleeping, sleeping
Your baby's sleeping, sleeping
Sleeping, sleeping
Sleeping, sleeping...

E          C#m  B
How many fantasies
Were interrupted by
A thousand galaxies
Drifting slowing by

A                C#m       B
The Mona Lisa's got you in awe
The Mona Lisa's got you in awe
The Mona Lisa's got you in awe
The Mona Lisa's got you in awe