I used to do the journey regularly, and agree with previous posters who have said that fast trains from Glasgow are much better than the Sleeper. That's noisy, with jerky stops and starts. The daytime trains are faster and smoother.
If you can make advance bookings - weeks ahead, as soon as booking opens -you have a much greater choice of fares and times - if possible, cheap first class makes all the difference. Avanti West Coast also do Standard Premium, which guarantees a table seat rather than an airline one. You can also get some bargains if you're prepared to travel /have meetings at odd times. Off-peak trains are a lot cheaper. I've caught a train around 8.30 am, worked hard on board all morning (wifi usually OK, though not perfect) , gone to a meeting at 2.00, had a quick drink with a friend at 6.00 and caught the 7.00 approx train and been back in Glasgow by midnight. It's a long day, but if only twice a month....
If you have to be at work 9 -5, cheap off-peak travel plus the lodgings suggestion mentioned above also seems worth thinking about.
I'd prefer either of the above to the Sleeper. And important to note, in bad weather etc, the Sleeper is often seriously delayed.
Timetables are frequently amended for mainline services at the moment, because of Covid, but Avanti has a website that lists changes.
Railcard info here: www.nationalrail.co.uk/times_fares/National-Railcards.aspx