We have just been in Gunung Mulu National Park. It has been awesome!
If you need a guide and the trips with National Park is fully booked or they do not have on the dates that you want, I really recommend to look for JENNY. She is a freelance who organise whatever you need ( accommodation, transport, private tours, and so on) with a very affordable price, sometimes cheaper than the HQ National Park.
You can find all her details below:
Mobile number: 0060128510441
We are just a normal couple, not extremely fit, just normal. We tried to climb the Summit, but it was just IMPOSSIBLE, please, do not even try unless you are very very fit. However, we tried and we made the PINACLES TREKKING, what was awesome but very hard... I am not going to lie, at one point I thought I would die lol. It is quite dangerous, specially at the end, but well... give it a go!
Hope all this help someone!