I understand the how, I just simply can't manage to achieve a splice.

I come stuck when feeding the core back through the jacket every time. I cannot get the core more than 2 or 3 cm past where the core comes out of the jacket and that to me does not feel like it is enough. I know you can stitch/whip it but you would now be relying purely on the cotton for strength.

It doesn't matter what or where I buy the rope from and I am using Selma Fids (not cheap, but cheap fids aren't any better or worse).

What other options are there other than tying a hitch or bowline? Every couple of years when I replace the line I have the same dilemma and end up just tying something like halyard hitch.

Not sure if this is what your describing but I was having trouble getting the core to bury in past the eye very far by milking the cover alone. I now manipulate the eye by pulling against it with a spike or screw driver as well and it seems to bury the core well past the eye and deep into the line.