Why do you assume you will need an amplifier? Since switchover (assuming you are in a post switchover area) it is extremely rare to have to use an amp. Signal level is rarely an issue, signal quality is paramount.
Reading posts on this forum it is apparent that many people don't understand this so look at it this way. In the analogue days a signal level of 65(ish) dBmV was required to produce a good picture, the digital signals were roughly 20dB lower than the analogue signals and were able to be processed perfectly adequately. At switchover the output levels were increased to around the levels of the old analogue signals so even using an 8 way splitter (losses around 12dB) you still have 8dB signal more than you know the tuner needs to work WITH NO AMPLIFICATION.
You need to collect good signal (as your description of the aerial implies you have), deliver it to your distribution point as cleanly as possible by using good quality screened cable (RG6 as a minimum, CT100 ideal but expensive), split it efficiently (four way f type splitter from your description) then deliver it to the tv tuner as efficiently as possible (preferably direct into the tv but if you must use wall plates make sure the cable does not get kinked or bent which is almost impossible hence my dislike of wall plates). Simple, efficient, cheap and effective.
I have quite happily used 8 way splitters off an indoor aerial with no amplification, nowadays I rarely need to use amplifiers in fact I would say I remove unecessary amplifiers roughly in the ratio of 20:1 compared to the number of new that I supply. Obviously I have a big advantage in being able to measure the signal quality of the signals I am dealing with but the main point is is that amplification is becoming less and less necessary and I would suggest that the assumption should be that it is not required. If you have followed the above good practice and you are getting pixelation then (ideally) use a masthead amp (f type splitters have power pass legs) or a basic one way set back amp between the aerial and the splitter.
Additionally, incorrect amplification can destroy a good signal.