There is a huge # of weather websites, mostly offering the U.S. run GFS model because the UK Met Office doesn't release much from its own model.
NOAA is one favourite of mine.
BTW, SB, the SigWx charts do not show cloud tops. I used to think they did, but I was very wrong, as I discovered on a number of occassions when the SigWx was clean but there was solid IMC to FL190 or so
The scalloped areas on the SigWx show
hazardous stuff like icing and turbulence or whatever and do not relate in any way to vertical cloud extent.
There are however websites which show cloud tops, derived from GFS. The NOAA one above offers Soundings which are fairly easy to interpret for where the IMC will be vertically.
For VFR flight, one needs the tafs and metars (both ends and near-enroute airports) and not a lot more... the MSLP charts show the weather trends.
For IFR flight, one needs potentially a lot more information unless flying something very capable, and that is where more extensive data comes in. For example I scrap any flight where the forecasts show that the cloud tops will be above FL160 (my ceiling is FL200) or where there will be significant icing risk in the terminal areas.
One could write for hours on this stuff but the OP posted a one-liner.