pressure loss going from 1" supply to 3/4" supply to home, 120 feet length
As you now realize, going from 1" steel pipe to 3/4" PEX is a big step down.  1" steel pipe has an actual ID of 1.05" and 3/4" PEX has an actual ID of 0.68".  At a flow of 8 gallons per minute, the pressure loss for 1" steel is 1.9 PSI/100' and the pressure loss for 3/4" PEX at that flow is 12.3 PSI/100'.  What you did was the equivalent of stepping down approximately two sizes.

1" PEX will still give less than your previous pipe but it might be acceptable.  The pressure loss of 1" PEX at 8 GPM is 4.2 PSI/100' and the pressure loss of 1-1/4" PEX at 8 GPM is 1.6 PSI/100'.  You will have to decide what you want as far as price vs. performance.

EDIT:  You might consider if another material would be suitable, such as 1" SCH 40 PVC.  1" SCH 40 PVC has losses similar to 1" galvanized.