After reading this thread, I'm thinking if I should purchase an SDS drill, will that help in drilling the holes or won't it just be the same issue?
No fines walls are a royal PIA (but then you know that), and even with an SDS the drill can still move slightly out of line when you start drilling, but once started they will generally drill relatively straight and go through the stones with less opening up of the hole than you'll ever get with a mechanical impact drill. I have found that the improved/extra-flute drill bits such as the
Bosch 3-flute, deWalt Xtreme 2 4-flute, Hilti 4-flute (picked-up from eBay), etc drill truer holes in no-fines and coarse aggregate concrete, but you may still need to employ tricks such as first drilling a 5.5mm hole when you need a 7mm hole (e.g. for a brown plug), then enlarging if required. Just avoid cheap/no-name SDS bits - not all SDS bits are equal! In the event your hole is still a tad large, you can always glue your plugs into the hole with some GripFil, or similar grip adhesive and leave it to go off overnight - just avoid the non-solvent versions as they are not as effective
In terms of a drill, there are a number of options - it is still possible to pick-up a new no-name SDS on eBay for £45 to £50, like
this one (although the cheap SFX one might be a better bit as you have a long window to return it, should it die), FFX (a well-known tool retailer with a good reputation) now sell their own
low-cost SDS (Chinese import) for under £60, whilst to get a
blue Bosch (i.e. the industrial range, not the DIY range) you'll pay in the £70 to £80 region for a basic model (so not that much more than a hulking great 7kg monster), although personally I'd go up a bit to about the ton mark and get a GBH2-24, which is a far better performer (I've had one, and they do what it says on the can...). Apart from Bosch blue, other good brands include Makita, Hikoki (was Hitachi) and deWalt.
Leave the overweight numb monsters for breaking out brickwork and concrete - a 2kg class (I.e. 2 to 3kg weight) SDS will do most of the work you'll ever need, they all have rotation stop these days (so they'll do concrete and brick chiseling as well as tile removal) and the weight won't kill you. Whatever you buy look for ideally 2J (joules) hammer force and above, and don't get too hung up about the motor wattage (which is much less of a factor with SDS drills) - BTW the Chinese tend to overquote both of these enormously
. 
