The 1040SR is new starting in 2019.  It is the same as the regular 1040 just larger type and the Standard Deduction chart is added to page 1.  But has the same line numbers.    You automatically get the SR if you are 65.  If you are using the Desktop program there is a way to force the one you want.

Even the regular 2019 1040 return is now different than 2018.  They changed the line numbers again and reduced the new schedules from 6 to 3.

1040SR https://www.irs.gov/pub/irs-pdf/f1040s.pdf

1040 https://www.irs.gov/pub/irs-pdf/f1040.pdf

If you use the Desktop program you can switch to forms and the Info Wks part II has a selection to select 1040SR or not.  You can not change it in the Online versions.   In the Online version if you want to use the regular 1040 form, you can print out the 1040SR and copy the amounts onto the 1040 and then mail your return.

If one of you is 65 or older then the 1040SR is generated and that is OK ... as stated above the forms are IDENTICAL except for the font and a useless chart on the bottom of page 1.  This is the most useless thing the IRS has done to date ... they should have just increased the font on the reg 1040 form and not put out the 1040SR at all.