Personally, I have a little checkbook program that I use to keep track of my spending and balance. Like you -- and I presume like most people -- I have certain recurring bills: the mortgage, insurance payments, car payment, etc. I simply enter these into the checkbook program about a month before the bill is due. Then I can run a transaction list that shows the date, amount, and remaining balance after each transaction. So if I want to know how much money I really have available to spend, I just look for the last transaction before my next payday, and see what the balance will be on that day.
Personally, I always keep a certain amount of pad in my account so if I made a mistake and entered an incorrect amount for a check, or forgot to enter one completely, I don't overdraw the account. (I like to keep $1000 in such padding but that's way more than really necessary, it's very rare that I make a mistake of more than $100.)
In my case, I don't enter electric bills or heating bills because I don't know the amount until I get the bill, and the amounts fall well within my padding, and for just two bills I can factor them in in my head.
BTW I wrote this program myself but I'm sure there are similar products on the market. I used to use a spreadsheet and that worked pretty well. (Mainly I wrote the program because I have a tiny side business that I have to keep tax records for even though it makes almost no money.) You could in principle do it on paper, but the catch to that is that when you write payments on your paper ledger in advance of actually writing the check, you will often be writing down payments out of order, and so it becomes difficult to see what your balance is or was or will be on any given date. But a computer system can easily accept transactions out of order and then sort them and re-do the balance calculations in a fraction of a second.