Hi Radziah,
It's lovely to see you having fun in the pool!
You already have a developed a good monofin technique, good job!
I do not know what your budget is, but I would say your competence warrants to have the best fins you can or want to buy. Fins like a tailor made Startfins - Build by Alex. If you're on a budget, and you want to dip your toe in a fin, while you safe up for a top of the line model, you'll be greatly served by either the Waterway Nemo (E 224.72 ), or the Specialfins Freediving monofin coloured (E 269,-) (mailing cost excluded). With shipping cost it may turn out Specialfins may be the same price or cheaper then the Nemo, inquire I say.
What stiffness you ask? With your technique, and apparent strength: you Can handle medium. However you may be into swimming long distances, hours, then a softer blade makes sense. On the other hand if you like to go deep in CWT, 30+ meters, then a medium blade is better.
The Nemo and the Speciafins Monofin Colored differ in stiffness. The Nemo is a bit more stiff. Taking both fins in a blade stiffness order:
Specf. soft, Nemo soft, Specf. med, Nemo med, Specf. hard, Nemo hard, Specf. extra hard.
I would avoid the Specialfins soft, because that one may have durability issues with it's too thin blade.
The rest of the fins are good.
About the footpocket angle, it really does make a big difference, to all users - beginners and pros. What does it do? It makes for easier swimming and
much longer gliding. The Nemo has 12 degrees and the Speciafins 15. A bonuspoint for the Specialfins I think.
From this I think the Speciafins Monofin Colored - medium stiffness looks to like the best, with the Nemo medium next in line.
One additional nicety with the Speciafins is that you can choose a color, maybe it matches your suit's color
Bright colors are safer for deep-diving, making for easier spotting.
As a final note, about choosing a top of the line 'Hyperfin' model, such as Starfins offers (
http://starfins.com/eng/), there are some alternatives emerging, foil and fluke fins. The Dol-fin foil offers a very durable construction and hyperfin level performance. The Lunocet 2015 fluke promises a good performance, but it is not proven, and suffers from bad delivery times. But since you ask about the extra money for the speciafins medium is worth it, I would say yes because in order of importance: 1 more angle (+25% / + 3 degrees), a bit softer then the Nemo medium, nice color blades.
I hope this helps, and when you get your fin I love to see a video of you using it!
Love, Courage and Water,
Kars