My accountant said just make all contributions from the same account. It doesn’t even have to be the business account per him (since I’m a sole proprietor), but that helps with accounting.
I mostly do traditional contributions because it helps me maximize the pass-through deduction, but if I get my taxable income to the limit ($320k?) then I do roth contributions. I usually don’t know about that until after I do my taxes, but apparently you just have to elect (ie, say you will) to make your contributions by the end of the year, not actually make them. So you can do all your taxes and then figure out how much of the remaining total amount you elected to make should be traditional vs roth contributions. So all year I make after-tax contributions and come Jan/Feb/March I make some roth contributions for the prior tax year depending on how my taxes looked. Hope that made sense…