Improving meditation quality

Personally I'd prefer doing a single session, but my problem is my foot falls asleep after 20 mins., so maybe I should try your 2x20 idea. One benefit perhaps would be a chance to do two different styles, each one tailored to how you generally feel at that time of day.

 

Ive been doing meditation for years now and I find self-guided to be ineffective. The actual approach should be a personal thing imo and you may find it varies from day to day. Also I wouldn't use audio or mantra, at least not at an advanced level.
There are books out there that offer suggestions on breathing techniques but the outcome is always the same - to be present. So the ritual isn't that important.

I find getting myself in the mood first before I practice is the most important thing, rather than have a hundred thoughts bouncing around and then do it. For example just sitting and looking at some object for a while so I can feel present. You see when you close your eyes the mind can get confused given it's still daytime, then thoughts can run wild. This is what most people struggle with. So preparation is key. Personally I wouldn't do it at lunch time either but late after noon. And you say it takes you 20mins at a time, I can't imagine doing it in 20mins. It takes me an hour.

Here's a book I read that gives a guide on breathing techniques:
https://www.amazon.com/Mindfulness-Breathing-Manual-Serious-Beginners/dp/0861711114
The terminology is a bit strange and it's modeled on Anapanasati style.

There's a mediation guru, John Butler who's written books at a more simplistic and philosophical level. I've watched a lot of his videos and they've helped be demystify it if you're interested.
https://www.youtube.com/@SpiritualUnfoldment
I find having an understanding at a deeper level is essential. Understanding for example what a pure state of consciousness actually is compared to what we think is real, ie: our Ego. It's our ego that causes all the tension and unrest.

 

Try so called "mini meditations". For beginners, the biggest issue is to make your mind shut up. Your mind have such a momentum that instead of trying to focus for 20 minutes it may be a better idea to just decide to take 3 deep breaths multiple times during the day. This will create some space for you and is a great beginning.

Guided meditations can be helpful in the very beginning but the best thing is to not rely on them for too long. It will be harder to meditate deeply if you only rely on guided meditations. It is a good way to learn how it works though.

Buy a copy of "The power of now". Read one page in it before sitting down. I find it really helpful. It contains a lot of pointers. "stillness speaks" and "Tao Te Ching" are also good books. "A course in miracles" is actually a step by step guide you could use. I think it contains 800 lessons or so. If you stick with it for 800 days, you should have at least grasped what meditation is all about.

I recommend not lying down too much when meditating. The lotus position and half lotus is considered very stable positions. You will be more focused than in any other position. Lying down makes it harder to not wander away into daydream or even falling asleep completely. If you have a lot of neck/back pain like me you may not have any other option anyways. It is better to meditate for 3 minutes and focus 100% than to push yourself trough 20 minutes just for the sake of it. It is better to meditate 3 minutes five times during the day than doing 20 minutes once. True meditation is just about getting skilled in letting go. Letting go of everything. Even the desire to reach any particular state.