Please, a little help on where to post this?

I am very new to the travel miles/credit card points for travel game and could use some advice on an upcoming trip. Next year (2019) is my 15 year wedding anniversary and we have decided to go to Italy for a few weeks taking our 9 year old daughter. We are originating from Orlando, FL. I was looking at trying to fly into Venice on June 4 (overnight arrive June 5) and leave from Rome on June 24. We have booked a cruise already that leaves out of Rome on June 16 and returns on June 23rd. So, the dates are flexible by a few days later, but not earlier.

I signed up for a couple Chase cards recently and by next month will have about 120k Ultimate Rewards points. One of the cards is the Sapphire Reserve, so I can redeem at 1.5 cents per point on their travel portal. I'm fine with economy for the connecting flights, but would really like to see if I can get some sleep on the longer portion to be more rested when I arrive in Italy. To that end, I am wondering what my options are for getting a business class lay flat seat for the long portion of the flight across the Atlantic. I know I don't have enough miles to book 3 business class tickets. Is it possible to book the tickets in Economy and use miles to upgrade the one leg to business for all 3 tickets? Or am I forced to upgrade the whole round trip ticket? Or is it possible to book economy tickets with miles and pay to upgrade the one leg to business? If I call an airline booking agent, can they mix and match the cabins like this for a cheaper price/miles? Which airlines should I even be looking at? I know my Chase UR points can transfer to some airlines and then those can be used on partner airlines. I have been tumbling down the rabbit hole researching that the last few days and I feel more confused than when I started.

TLDR - I need 3 tickets (2 adult, 1 child) in June 2019 from Orlando to Venice, returning Rome to Orlando. I have approx. 120k Chase Ultimate Rewards points. I would like to have business class (lay flat seats) for the leg across the Atlantic from the US to Europe; all other legs, including the transatlantic return leg, can be economy or premium economy. What are my options to use miles or miles+money to make this happen for the cheapest price?

Thanks for the help and advice.