I have a question about saddles. I bought a mountain bike 2 days ago. I thought it would be better to ride a bike rather than going on a walk in these Corona days (for exercise purpose). My bike is MOSSO Raceline 29" alloy frame. My weight is 138kg and my height is 1,95 cm. Bike shop guy recommended me this bike because I am overweight. When I ride the bike, the saddle gives me a lot of pain to my butt. I read forums, they say you'll get used to it in 2 weeks but I am not sure because of excess weight. I checked on the internet that there are some gel saddles (Selle Royal). But I am not sure which one will be comfortable and suitable for me. Please consider that I only ride on the bicycle on the road (not going mountain or unbalanced terrains), I use it like a road bike. If anyone has any saddle purchase experience can you please share it with me? Thanks for your help guys.
One cause is that you've mistaken the saddle for a seat. The main difference is that a saddle does not hold all your weight - some amount of your weight sits on the pedals and a small amount on the hands.
By comparison, a seat holds 100% of your weight, and you could ride with no weight on the feet or hands. This wouldn't work.
Other items that have saddles include horses and motorbikes (which have stirrups and footpegs respectively) whereas seats are at the dining-room table, in cars, and recumbents.
Suggestion try transferring some of your weight through the pedals rather than putting all your weight on the saddle. The downside of this is that its more pressure through your knees, which can cause aches.
Separately, the material of your saddle is a completely personal choice. Some people are perfectly happy with hard plastic or carbon saddle. Some people find a squishy padded saddle works best for them.
A Gel or heavily padded saddle will squish out from under your sit-bones (ischial tuberosity https://en.wikipedia.org/wiki/Ischial_tuberosity ) and will put pressure on the softer tissues. In more-extreme cases the padding will put pressure on your soft tissues, flesh that shouldn't be bearing any weight. This is one of the causes of penile numbness in males and similar in female cyclists.
Just to be clear, your butt doesn't support your weight. Your sit-bones, part of your skeleton hold basically all your weight.
Another thought is perhaps your existing saddle is the wrong width for your sit-bones. On a too-narrow saddle your sit bones will hang off the side, causing weight to be held on the soft flesh. If your saddle is too wide, its not quite as bad. There are a couple of existing questions with answers on this topic already: