I am the same age and like stage as you- hoping to start ttc in the next year.
I have taught for 9 years and am in primary. I have a middle management role after similar deliberating...
I considered the best way to go for quite a bit before my UPS/ middle leader meeting.
Firstly wondering if it's best to climb the ladder as much as possible pre children for max pay and less pressure to then be progressing/moving jobs after when you have a family. Equally if it's worth progressing for what is not much pay always and if it is truly what I want or just what I think is expected of me.
In the end my thoughts are that I want to get myself into a role pre baby which balances good pay, manageable workload and career satisfaction (recognising sometimes reward comes with hard work and a bit of short term pain but I don't want to be burnt out). I also want it to be relatively manageable coming back post baby and realistically it's going to be a few years balancing things around v young family. For me, full time class teaching with no other focuses was extremely full on and I needed the more whole school overview role to keep me motivated.
I feel the workload around this completely depends on your school though. Mine gives a good amount of regular time each week for middle management roles out of class. It also pays extra for subject responsibility/leadership roles on top of just UPS banding. I have then also continued climbing the UPS scale. This makes it all worth it for me financially. I know not all schools do this. I do feel some of our middle management roles are actually more manageable than being a full time class teacher- probably does depend on the person though. There is also the factor to consider that UPS can make you very expensive should you wish to move schools. I'm happy where I am so decided this isn't a problem for me.
As I have got more experienced I have found there are some class teacher requirements which you learn to cut corners on without impacting pupils, I spend a lot less time on planning etc as I have the basics there and just adjust or innovate. But there are lots of ongoing, inflexible nonnegotiables in class. As well as it being relentless and exhausting especially if you are lower primary.
With my management role bits i am a bit more office based in parts of the week and this work can be prioritised depending on what else is going on that week as lots of it is long term development work. I don't find it stressful in the same way.
But that's me- you know your school and what will make you feel satisfied. You are right £50-100 per month if it is a lot more work and compromising your life satisfaction js not worth it. There is absolutely nothing wrong with being a class teacher. It doesn't mean post children you can't then progress if you want. Lots of people don't go into teaching until later and your class teaching is building up lots of experience.
Hope this ramble of my perspective/thoughts helps!!