You are writing in a very indirect style which I suspect may be a polite form of speech in your native language. In English these types of construction are less common and sound very unnatural. Try to use simpler forms: "It was a warm and joyful time..." is perfectly OK and sounds more natural. The use of "I suppose" is not correct in your sentence in any case. If you were to use this style, you would write "I found it to be...", but again I would discourage you from saying it this way because it appears contrived to a native speaker.
Similarly, "I would be very glad if you could suggest how to change this sentence to convey my meaning more clearly." is the correct form.