Welcome to the forum Purpletrain.
If you reckon you can generally rely on getting these specific trains every day, consider buying
advance tickets each day. These tickets include seat reservations so you would be guaranteed a seat every day too. Even if you miss the booked train one day a week (staying at work later than planned etc) and have to buy a day ticket, it's still cheaper than a weekly or season ticket. It also means you don't need to pay for the train on days off and holidays.
TPE trains between MAN and SHF are busy but if you want a seat, there are few seats in
Coach C between First Class and the driver's cab which tend to remain available as people think this area is First Class!
Also do you have a 16-25 Railcard? If so you can get 50% off advance tickets via
www.tpexpress.co.uk only as opposed to the usual 34%.
I used to do this commute daily for a year in the opposite direction so send me a PM if you want further advice