Well, here is what the website (
https://www.bintelshop.com.au/welcome.htm ) says:-
- Eyepieces: 26mm Wide View (2"),15mm and 9mm Fully Multi-coated Plossl (1.25").
- Moon filter 1.25" for improved Lunar contrast and detail
Now, a bit of research into these eyepieces on the Bintel site can be done. They are:-
Bintel FMC 26mm (2")
Bintel Plossl 15mm (1.25")
Bintel Plossl 09mm (1.25")
I think the first you you will quickly decide needs replacing is the 9mm plossl. Many find the eye relief to be too small. So you could search for a 9 or 10mm longer eye relief design.
Or, as you are suggesting, get a barlow lens. The Bintel Barlow 2x ED (2") on the Bintel site for $89 will get you started. You might want better quality (more expensive!) later on. And that will allow you to use the 15mm eyepiece with its better eyerelief, but have an effective 7.5mm eyepiece with that doubled magnification.