1. Are there simple remotes capable to learn and accept single button code by entering pressing button certain number of times? (Instead IR->IR)
Yes, most OneForAll remotes can modified in the following way:  
A.  Assign a Samsung TV setup code to the TV button.  For example 0618 or 0702.
B. Then, Press Setup (or Magic) until 2 blinks
C.  Enter 994  (2 blinks)
D. Tap Setup
E.  Enter 00081 
F.  Tap a button of your choosing (e.g.  PIP CH+) 
The remote will blink twice, and now  PIP Ch+ will send the discrete signal to switch the TV input to HDMI1.  In step E, use 00030 for HDMI2, 00175 for HDMI3, and 00176 for HDMI4.


2. Are there such codes available for Samsung TV discreet input function? Perhaps a year ago ... but my search was the unsuccessful, until I happily noticed that one Samsung PC monitor/TV had direct HDMI button on remote.

The search function on this website shows this post for Samsung TV IR codes.  In general, you need to use RemoteMaster software to convert function numbers into the 5 digit code used step E above, but Post 65 of the linked thread lists most of the possibilities.

If you decide to try one of these remotes, post back the model you're thinking of and I'll probably be able to tell you if it is suitable.   Samsung is easy because it is a major brand.  The 5 digit code only affects the function number, but the remote already needs to have a setup code with the correct IR protocol and device numbers built in.  Of course this will be the case for major brands.