Paddington to Penzance

Hi all,
Hoping someone on here can help me out….
I commute from Norbiton to Penzance on Thursday each week. I finish work at Norbiton at 17:30 and am literally just across the road from the station.

Recently due to being owed Time off in lieu I have been able to finish earlier and had the luxury of being able to get advance tickets for the 15:06 from Paddington. Unfortunately this has come to an end, and from 29th June I am back to looking at Peak time trains.
I have a Devon and Cornwall railcard, which covers me from Tiverton Parkway to Penzance in theory, but am struggling to make much use of it at the moment.

Can any of you clever people find any reasonable tickets for this route? I am not averse to the sleeper (seat), but cheapest I can get that seems to be £55 if I book early enough.
I have also used Clapham Junction to Exeter St. Davids before, but that doesn't tend to work for this time in the evening for onward connections.

I used to do Megabus to Plymouth overnight, but the walk to Plymouth for the first train to Penzance was not ideal, and I prefer the train as there is room to move about once it is past Exeter.
Don’t mind changing trains or wait at Exeter for example.
When you consider the distance involved, then £55 to Penzance isn’t bad, but can’t help feel that I am missing something

For completeness my return journey is 15:00 Penzance to Paddington on Sunday, but that can generally be had for £23 without using the railcard.
Sorry for the lengthy post but wanted to include as much info as possible.
Many thanks
Steve

trainsplit.com doesn't suggest anything more complex than the £113.70 Standard Super Off-Peak Return (SSR) Norbiton - Penzance Route ✠ Any Permitted with suggested itineraries:

Thursdays
1735 Norbiton - Waterloo 1805
Tube Waterloo - Paddington
1903 Paddington - Penzance 0045

Sundays
1500 Penzance - Reading 1949
2024 Reading - Twickenham 2122
2145 Twickenham - Norbiton 2206

The Sunday suggestion seems very slow after Reading. I would consider via Paddington and Waterloo or using the District Line Paddington - Wimbledon. The £113.70 ticket is valid by any of these routes.

Given that Gnasher had found an itinerary for about £80 return I don't think a £113 one would be much use - even the flexibility doesn't help much as there's only really the 16:03 train on a Sunday that is of any extra use (there's no later train on the Thursday, and later trains from Cornwall would get in too late to get a good night's sleep before work)