Hi there,
I'm gonna tell you the truth: there's not any "proven well converting sales funnel" at all!
Don't waste time on that question, is the wrong question you're asking yourself.

As the founder of a Conversion Rate Optimization company, having worked on hundreds of different websites and e-commerce and having brought hundreds of millions of additional revenue optimizing checkout processes and conversion funnel ..

Here's the delusion: what works on a website doesn't work on another website.

Why? Because it's a different story and it should be treated accordingly.
If you have the brand awareness of Amazon there are stuff and strategy that works there, that are not the same stuff and strategies that will work on your website.

So the question you should ask yourself is: what would build so much-value for my customer and so much so that they will take the next step towards the funnel until they reach the macro-conversion I want them to take?

Here a few hint to understand your customer mind and then translate those finding into actual concrete ideas that will lead your website to an increased conversion rate:
1. Use tools such as "qualaroo" to survey your customer on the funnel, especially the visitors that shows an exit intent;
2. Run an usability testing trough usertesting or similar to understand their thought and feeling while surfing your website;
3. Configure a funnel in google analytics and check which step of the funnel are loosing the most customer, then run a survey on that page and run ab test accordingly to your findings.

A couple of advice for your website:
1. There's not a clear unique value proposition: why should I buy from you rather then the competition?
2. I can't see any reference to shipping cost and delivery estimates on the checkout, this is something your users want to now "upfront";
3. Add a guest checkout feature, forcing a sign-up might prevent your customers to buy (check on analytics as well).

Those ideas are the first one that came to my mind in 5 minutes ;)

Good luck!

Luca

Can you please provide a bit more clarity?
Are you looking to increase average order value? With tactics like up sells and cross sells?
Are you looking to optimize your 5 step shirt design funnel?
What does your current funnel look like?

I could help you. Worked with a friend on a sales funnel a few months ago using best in class practices. My rate is very low.
Looking at your website, it seems to me you don't have an onboarding process. You're just showing the shirts. Not underlining what you're good at and so on so forth...

if you want we can do a quick call. Afterwards, I can provide you with a whole plan / model

A good funnel can make people aware of your business and turn them into repeat customers. Where both video and text are available on the same page, 72% of people in one survey would rather use video to learn about a product or service. This kind of content introduces the brand to its visitors by helping them learn how to save money and do jobs themselves.
You can read more here: https://sumo.com/stories/ecommerce-marketing-funnel
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath