My MK3 Golf 1.4L isn't running at it's best if I'm honest

It seems to run OK when it's cold but as soon as it gets warm acceleration drops considerably and any slope/hill i've had it. Revs drop fast and I'm lucky if I'm doing 15/20mph up a hill. Quite embarrassing when you have people flashing you behind you because you are going too slowly!

The engine has a ticking sound which doesn't sound very healthy and the oil pressure light is on most of the time (changed sensor and has plenty of oil, never lost oil) so I'm assuming I'm just losing pressure. My dad being a mechanic told me the engine is getting tight when it warms up putting stress on the engine causing it to lose so much performance.
To the point, I'm considering changing my 1.4 petrol engine to a 1.6L golf mk3 engine of the same year. It's only done 73,000 mile which is around 15,000 less than mine.
Would this be possible? Almost a "straight swap" if you will? or will I come across a lot of problems? I was going to opt for a 2.0 GTI engine but my dad told me that would be too much hassle and the insurance would go up a lot when I declare it being only 19 an all! The jump to a 1.6 doesn't cost me that much more on the £2000 premium I already pay so i thought why not

What do you think?